Andrea Sikon, MD, FACP

Advances in our understanding of the pathogenesis of cervical cancer, new tests for human papillomavirus (HPV), and the development of HPV vaccines in the last decade are transforming the way we screen for cervical cancer.

As a result, screening guidelines are evolving rapidly, requiring clinicians to keep up-to-date with the evidence and rationales supporting the latest guidelines to properly convey best practices to patients.^1–3

For example, we must understand why it is safe to extend the screening interval in women at low risk (as recommended in the new guidelines), and we need to be familiar with the options for women who test positive for HPV. Patients and providers may often find such new recommendations frustrating, and patients may feel that they are being denied something necessary by insurers rather than being treated according to scientific evidence.

This article will review the newest screening guidelines and the evidence supporting these recommendations for primary care providers. We will also review the potential role of novel biomarkers, newer HPV tests, and possible future strategies for cervical cancer screening.

WHAT’S NEW IN THE LATEST SCREENING GUIDELINES

Over the years, various organizations have issued separate screening guidelines, sometimes agreeing with each other, sometimes disagreeing.⁴ Now, for the first time, several of these organizations have developed guidelines collaboratively, and we have consensus in the screening recommendations.

Shortly after the American Congress of Obstetricians and Gynecologists (ACOG) issued its screening guidelines in December 2009,¹ the American Cancer Society (ACS), American Society for Colposcopy and Cervical Pathology (ASCCP), and American Society for Clinical Pathology (ASCP) convened an expert panel to review the available evidence and develop a new joint screening guideline. Concurrently, the US Preventive Services Task Force (USPSTF) commissioned a targeted systematic review of the latest evidence.

Both the ACS/ASCCP/ASCP group² and the USPSTF³ released their new guidelines on March 14, 2012. In November 2012, ACOG issued its latest recommendation on cervical cancer screening.⁴ The following discussion highlights the consensus recommendations from these organizations (Table 1).

These guidelines apply to the general population only. They do not apply to women at high risk who may require more intensive screening, such as those who have a history of cervical cancer, are immunocompromised (eg, positive for human immunodeficiency virus [HIV]), or were exposed in utero to diethylstilbestrol.

Start screening at age 21

According to the new guidelines, women younger than 21 years should not be screened, regardless of the age at which they start having sex.^1–3 This is a change from the 2002 and 2003 ACS recommendations, which said screening should begin 3 years after the onset of vaginal intercourse.^5,6

Evidence. The rationale for the recommendation not to screen before age 21 stems from two pieces of evidence:

• Invasive cervical cancer is rare in this age group.⁷
• Screening can cause harm. For example, unnecessary treatment of preinvasive lesions can lead to long-term complications such as cervical stenosis, preterm delivery, and preterm premature rupture of membranes.^8,9

Additionally, one study found that screening before age 21 has little or no impact on the incidence of invasive cervical cancer.¹⁰

Longer screening intervals

The 2012 ACS/ASCCP/ASCP guidelines² and the latest ACOG guidelines⁴ lengthen the interval between cytology (Papanicolaou) testing to every 3 years in women age 21 to 29. Previous recommendations from these groups were to screen every 2 years, and the USPSTF first recommended the 3-year interval in 2003.¹¹

For women age 30 to 65, the ACS/ASCCP/ASCP, ACOG, and the USPSTF now recommend screening every 5 years if the patient’s results on combined cytology and HPV testing are negative. However, cytologic testing alone every 3 years is also acceptable.^2–4

Evidence. The evidence supporting a 3-year screening interval in women age 21 to 29 is primarily from modeling studies—no randomized clinical trial has been done. These studies found no significant difference in outcomes with a 2-year vs a 3-year screening interval.^12,13 In particular, the predicted lifetime risk of cervical cancer in women screened every 3 years was 5 to 8 new cases of cancer per 1,000 women, compared with 4 to 6 cases per 1,000 women screened every 2 years.¹⁴

Similarly, screening women younger than age 30 at 2-year or 3-year intervals carried the same predicted lifetime risk of death from cervical cancer of 0.05 per 1,000 women, yet women screened every 2 years underwent 40% more colposcopies than those screened every 3 years.² Therefore, screening every 3 years offers the best balance of benefits and risks in this age group.

Adding HPV testing to cytologic testing increases the sensitivity of screening—thus the recommendation to lengthen the screening interval to every 5 years in women age 30 to 65 who are at low risk and who have negative results on both tests. (Previously, the interval was 3 years.)

Specifically, adding HPV testing improves the sensitivity of screening for cervical intraepithelial neoplasia grade 3 (CIN3), so that, in subsequent rounds of screening, fewer cases of CIN3 or worse (CIN3+) or cancer are detected.^15–17 The longer diagnostic lead time with combined testing is associated with a lower risk of CIN3+ or cancer following a double-negative test result than screening with cytology alone at shorter intervals. Combined testing at 5-year intervals is associated with a similar or lower cancer risk than cytology-alone screening at 3-year intervals.⁹

Moreover, modeling studies have shown that combined testing of women age 30 and older at 5-year intervals leads to fewer colposcopies and a similar or lower cancer risk than with cytology screening at 3-year intervals.^18,19

Combined cytologic and HPV testing has received its strongest endorsement to date from the ACS/ASCCP/ASCP, ACOG, and USPSTF in their latest guidelines.^2–4

In 2003, ACOG gave HPV and cytology combined testing an “optional” recommendation for women over age 30; in 2009, it upgraded its recommendation to the highest level of recommendation.¹ At that time, the USPSTF did not recommend for or against HPV testing, while the ACS did recommend HPV testing (with cytology testing alone every 2 to 3 years as an alternative screening strategy).⁵

Now, the ACS/ASCCP/ASCP and ACOG recommend HPV and cytology combined testing as the preferred strategy for screening women age 30 or over.^2,4 Similarly, the USPSTF gives combined testing for women age 30 to 65 a grade A (its highest) recommendation.³ (In 2003, it had given it a grade I—insufficient evidence to assess the balance of benefit and harm.)

Evidence. Several recent studies provide compelling evidence that HPV testing has high sensitivity and excellent negative predictive value, supporting the stronger endorsement of HPV testing and longer screening intervals.

The Joint European Cohort study,²⁰ in 24,295 women, conclusively showed that the 6-year risk of CIN3+ following a negative HPV test was significantly lower than that following a negative cytology result alone (0.27% vs 0.97%).

Katki et al,²¹ in another retrospective study, analyzed data from 330,000 women age 30 and older who underwent combined HPV and cytology testing. Looking at the tests separately, they found the risk of CIN3+ was comparable in the 3 years following a negative cytology test by itself and in the 5 years following negative combined HPV and cytology testing. In fact, combined testing at 5- or 6-year intervals offered better protection than cytology alone at 3-year intervals.

Furthermore, combined testing is also more sensitive for detecting cervical adenocarcinoma.²² (Most cancers of the cervix are squamous cell carcinomas, but approximately 10% are adenocarcinomas.)

Stop screening sooner

In 2002, the ACS recommended ending screening at age 70,¹¹ and in 2009 ACOG said to stop at age 65 to 70.¹ Now, the ACS/ASCCP/ASCP group² and ACOG⁴ recommend stopping screening sooner—at age 65—provided that:

• The patient has had adequate negative screening until then. (Adequate negative prior screening is defined as three consecutive negative cytology results or two consecutive negative combined HPV and cytologic testing results within the 10 years before ceasing screening, with the most recent test performed within the last 5 years.)
• The patient has no history of CIN2+ within the last 20 years.
• The patient is not at high risk of cervical cancer, eg, no history of a high-grade precancerous cervical lesion or cervical cancer, in utero exposure to diethylstilbestrol, or immunosuppression (eg, HIV infection).

The USPSTF had already adopted this position.

Evidence. In women over age 65 who have had good screening, cervical cancer is rare and CIN2+ is uncommon.^2,23,24 Kulasingam et al,⁹ in a modeling study performed for the USPSTF, calculated that continuing to screen until age 90 prevents only 1.6 cancer cases and 0.5 cancer deaths and extends life expectancy by only 1 year per 1,000 women.

Other studies also suggest that newly acquired high-risk HPV infection in women age 65 or older is associated with a very low absolute risk of HPV persistence and CIN3+ progression.^25,26

In addition, cervical cancer takes a median of 20 to 25 years to develop after infection with high-risk HPV.² Also, continuing to screen this older population will detect only a very small number of new cases of CIN2+ and may lead to harm from overtreatment.

Finally, postmenopausal women often have smaller and less accessible cervical transformation zones that may require more interventions to obtain adequate samples and to treat.

Stop screening after hysterectomy

The ACS/ASCCP/ASCP group, ACOG, and the USPSTF reaffirmed their recommendation against screening in women who have had a hysterectomy with removal of the cervix for a reason other than cancer and who have had no history of CIN2+ or cervical cancer.^2–4

Evidence. Several lines of evidence suggest stopping screening after a woman has a hysterectomy. The incidence of vaginal cancer is extremely low,²⁷ and the positive predictive value of cytologic testing of the vaginal cuff for vaginal cancer was zero in one study.²⁸ Also, a large cross-sectional study of 5,330 screening cytology tests in women who had a hysterectomy found only one case of dysplasia and no cancer.²⁹

Continue to screen after HPV vaccination

For the first time since HPV vaccines were introduced in 2006, the ACS/ASCCP/ASCP, ACOG, and the USPSTF have had to consider what to do for vaccinated women. All of their new guidelines say to keep screening them.

Evidence. The currently available HPV vaccines protect against cervical cancer,³⁰ but only against cervical cancer caused by HPV types 16 and 18. Other oncogenic types of HPV exist, and the current vaccines do not protect against them.

Furthermore, many women are vaccinated who are already infected. In addition, as of 2010, only about 32% of eligible girls and women in the United States had received all three recommended doses of the vaccine.³¹ And modeling studies predict that the impact of the HPV vaccine will not be apparent for at least another decade.³²

HPV 16/18 genotyping

The ACS/ASCCP/ASCP and ACOG now recommend HPV 16/18 genotyping as a triage option in women who have positive results on HPV testing but negative cytology results, and immediate referral for colposcopy if the genotyping test is positive.² The alternative option in this situation is to repeat combined HPV and cytologic testing in 12 months.^2,33

Evidence. The standard tests for HPV can detect DNA from about a dozen of the oncogenic types of HPV depending on the test, but they do not tell you which one the patient has. This information may be relevant, since not all “high-risk” HPV types are equally bad. HPV 16 and HPV 18 are the worst of all, together accounting for more than 70% of cases of cervical cancer.

Large cohort studies^34,35 have shown that the risk of CIN3 reaches 10% over 1 to 4 years in women who test positive for HPV 16, and over 2 to 5 years if they test positive for HPV 18. This clinically relevant short-term risk supports immediate referral for colposcopy.

In March 2009, the US Food and Drug Administration (FDA) approved a test for HPV 16 and HPV 18—Cervista HPV 16/18 (Hologic, Bedford, MA).³⁶

More recently, researchers from the Addressing the Need for Advanced HPV Diagnostics (ATHENA) trial,³⁷ in 47,208 women, reported that they found CIN2+ in 11.4% of women who tested positive for either HPV 16 or HPV 18, and CIN3+ in 9.8%. Of those who were positive for HPV 16, 13.6% had CIN2+ and 11.7% had CIN3+.

WHAT’S COMING?

As we gain knowledge of the molecular oncogenesis of cervical cancer, we appreciate more the complex relation between HPV oncoproteins and cervical dysplasia. Recent studies demonstrated the clinical utility of detecting novel markers in women who have positive HPV results.^38,39

At present, however, there is insufficient evidence to integrate these strategies into our standard of care for cervical cancer screening.

Novel biomarkers: p16 and Ki-67

Although HPV testing is sensitive, it has poor specificity and positive predictive value.^40,41 In a primary screening setting, women with normal cytology results who test positive for high-risk HPV may carry a risk of only 3% to 7% for high-grade CIN.^42,43

HPV 16/18 genotyping can be useful in this situation (see above). However, not everyone who carries HPV 16 or 18 goes on to develop CIN or cancer.⁴⁴

A novel biomarker, p16, has been shown to be overexpressed in cervical dysplasia and associated with high-risk HPV oncogenic transformation. Another novel marker, Ki-67, can be regarded as a surrogate marker of deregulated cell proliferation (Figure 1).³⁸

A recent study reported that a combined test for both of these markers (dual-stained cytology) had a sensitivity of 91.9% for detecting CIN2+ and 96.4% for CIN3+. This test was also highly specific: 82.1% for CIN2+ and 76.9% for CIN3+.³⁸

An Italian randomized trial reported that p16 immunostaining improved the specificity of HPV testing in detecting CIN2+.⁴⁵

In addition, the European Equivocal or Mildly Abnormal Papanicolaou Cytology Study⁴⁶ found that the dual-stained cytology test had excellent sensitivity for CIN2+ in women with atypical squamous cells of undetermined significance (ASCUS) or low-grade squamous intraepithelial lesion (LSIL) cytology results (92.2% for ASCUS, 94.2% for LSIL). The specificity for CIN2+ in ASCUS and LSIL was 80.6% and 68%, respectively.

A US study also showed that the sensitivity and specificity to detect CIN3+ by using p16/Ki-67 were 97.2% and 60%, respectively, in women age 30 and older.⁴⁷

If confirmed in more studies, p16/Ki-67 dual staining could help us in deciding which women who have positive HPV but negative cytology results should be referred for colposcopy.

HPV oncogene E6/E7 mRNA testing

In October 2011, the FDA approved the clinical use of a new-generation HPV test, the Aptima HPV assay (Hologic Gen-Probe, San Diego, CA), which detects mRNA for the proteins E6 and E7 from high-risk HPV.³⁹

HPV E6/E7 mRNA expression has been found in virtually all HPV-positive cancer cases and demonstrates a stronger correlation with cervical disease than detection of HPV DNA.⁴⁸ High-risk HPV E6 and E7 proteins immortalize and malignantly transform infected cells by inhibiting two host cellular anticancer proteins, p53 and retinoblastoma protein (pRB).^44,49

The recent FDA approval was based on data from the CLEAR (Clinical Evaluation of Aptima HPV RNA) trial.³⁹ In this trial, in more than 11,000 women, the test was as sensitive for detecting CIN2+ as the HPV DNA-based test, and it was more specific. This advantage was statistically significant. The higher specificity may reduce the number of unnecessary colposcopies and allow for more effective management.^50,51

A promising future screening strategy: HPV testing first, then cytology

HPV testing is more sensitive than cytology, while cytology is more specific. Thus, it would be logical to test for HPV first, and then to perform cytologic testing in patients who have positive results on HPV testing.

In the past 5 years, several large randomized clinical trials within national screening programs in Italy, England, Sweden, and the Netherlands examined the value of a primary HPV-based screening strategy.^15–17,52 These studies confirmed the superior sensitivity of HPV testing for detection of CIN2+.

A large Canadian randomized trial⁵³ compared HPV testing and cytologic testing as screening tests in women age 30 to 69. HPV DNA testing was 94.6% sensitive in detecting CIN2 or CIN3, compared with 55.4% for cytology. The specificity of HPV testing was nearly as high as that of cytology, 94.1% vs 96.8%. Furthermore, HPV testing followed (in those positive for HPV) by cytology resulted in a lower referral rate for colposcopy than did either test alone (1.1% vs 2.9% with cytology alone or 6.1% with HPV testing alone).

More randomized trial data are needed to evaluate the validity of this promising new approach in varied populations. The HPV FOCAL trial is comparing HPV-then-cytology testing vs cytology-then (in women with ASCUS)-HPV testing.⁵⁴ In addition, the aforementioned novel biomarkers for HPV oncogenic activity may eventually play a greater role in primary screening.

With the latest evidence-based screening guidelines, we can implement a more sensitive and effective screening strategy for better prevention and early detection of cervical cancer. Newer cutting-edge molecular technologies appear promising; however, their cost-effectiveness needs to be further evaluated.

A MORAL AND ETHICAL RESPONSIBILITY

Our unscreened and underscreened populations carry a higher burden of cervical cancer and of death from cervical cancer. Identifying and reaching out to these women is our moral and ethical responsibility and yet poses the biggest challenge in screening. Arguably, this could have the most significant impact on rates of death from cervical cancer.

Innovative measures in overcoming healthcare barriers and in making testing cheaper will help to close the gap between well-screened and underscreened populations in the United States and globally. Examples would be a low-cost, point-of-care screening test for the general population, and a government-subsidized global vaccination program. It is entirely conceivable that women will no longer die from cervical cancer in the near future, thanks to global effective screening and preventive efforts through widespread HPV vaccination.

Advances in our understanding of the pathogenesis of cervical cancer, new tests for human papillomavirus (HPV), and the development of HPV vaccines in the last decade are transforming the way we screen for cervical cancer.

As a result, screening guidelines are evolving rapidly, requiring clinicians to keep up-to-date with the evidence and rationales supporting the latest guidelines to properly convey best practices to patients.^1–3

For example, we must understand why it is safe to extend the screening interval in women at low risk (as recommended in the new guidelines), and we need to be familiar with the options for women who test positive for HPV. Patients and providers may often find such new recommendations frustrating, and patients may feel that they are being denied something necessary by insurers rather than being treated according to scientific evidence.

This article will review the newest screening guidelines and the evidence supporting these recommendations for primary care providers. We will also review the potential role of novel biomarkers, newer HPV tests, and possible future strategies for cervical cancer screening.

WHAT’S NEW IN THE LATEST SCREENING GUIDELINES

Over the years, various organizations have issued separate screening guidelines, sometimes agreeing with each other, sometimes disagreeing.⁴ Now, for the first time, several of these organizations have developed guidelines collaboratively, and we have consensus in the screening recommendations.

Shortly after the American Congress of Obstetricians and Gynecologists (ACOG) issued its screening guidelines in December 2009,¹ the American Cancer Society (ACS), American Society for Colposcopy and Cervical Pathology (ASCCP), and American Society for Clinical Pathology (ASCP) convened an expert panel to review the available evidence and develop a new joint screening guideline. Concurrently, the US Preventive Services Task Force (USPSTF) commissioned a targeted systematic review of the latest evidence.

Both the ACS/ASCCP/ASCP group² and the USPSTF³ released their new guidelines on March 14, 2012. In November 2012, ACOG issued its latest recommendation on cervical cancer screening.⁴ The following discussion highlights the consensus recommendations from these organizations (Table 1).

These guidelines apply to the general population only. They do not apply to women at high risk who may require more intensive screening, such as those who have a history of cervical cancer, are immunocompromised (eg, positive for human immunodeficiency virus [HIV]), or were exposed in utero to diethylstilbestrol.

Start screening at age 21

According to the new guidelines, women younger than 21 years should not be screened, regardless of the age at which they start having sex.^1–3 This is a change from the 2002 and 2003 ACS recommendations, which said screening should begin 3 years after the onset of vaginal intercourse.^5,6

Evidence. The rationale for the recommendation not to screen before age 21 stems from two pieces of evidence:

• Invasive cervical cancer is rare in this age group.⁷
• Screening can cause harm. For example, unnecessary treatment of preinvasive lesions can lead to long-term complications such as cervical stenosis, preterm delivery, and preterm premature rupture of membranes.^8,9

Additionally, one study found that screening before age 21 has little or no impact on the incidence of invasive cervical cancer.¹⁰

Longer screening intervals

The 2012 ACS/ASCCP/ASCP guidelines² and the latest ACOG guidelines⁴ lengthen the interval between cytology (Papanicolaou) testing to every 3 years in women age 21 to 29. Previous recommendations from these groups were to screen every 2 years, and the USPSTF first recommended the 3-year interval in 2003.¹¹

For women age 30 to 65, the ACS/ASCCP/ASCP, ACOG, and the USPSTF now recommend screening every 5 years if the patient’s results on combined cytology and HPV testing are negative. However, cytologic testing alone every 3 years is also acceptable.^2–4

Evidence. The evidence supporting a 3-year screening interval in women age 21 to 29 is primarily from modeling studies—no randomized clinical trial has been done. These studies found no significant difference in outcomes with a 2-year vs a 3-year screening interval.^12,13 In particular, the predicted lifetime risk of cervical cancer in women screened every 3 years was 5 to 8 new cases of cancer per 1,000 women, compared with 4 to 6 cases per 1,000 women screened every 2 years.¹⁴

Similarly, screening women younger than age 30 at 2-year or 3-year intervals carried the same predicted lifetime risk of death from cervical cancer of 0.05 per 1,000 women, yet women screened every 2 years underwent 40% more colposcopies than those screened every 3 years.² Therefore, screening every 3 years offers the best balance of benefits and risks in this age group.

Adding HPV testing to cytologic testing increases the sensitivity of screening—thus the recommendation to lengthen the screening interval to every 5 years in women age 30 to 65 who are at low risk and who have negative results on both tests. (Previously, the interval was 3 years.)

Specifically, adding HPV testing improves the sensitivity of screening for cervical intraepithelial neoplasia grade 3 (CIN3), so that, in subsequent rounds of screening, fewer cases of CIN3 or worse (CIN3+) or cancer are detected.^15–17 The longer diagnostic lead time with combined testing is associated with a lower risk of CIN3+ or cancer following a double-negative test result than screening with cytology alone at shorter intervals. Combined testing at 5-year intervals is associated with a similar or lower cancer risk than cytology-alone screening at 3-year intervals.⁹

Moreover, modeling studies have shown that combined testing of women age 30 and older at 5-year intervals leads to fewer colposcopies and a similar or lower cancer risk than with cytology screening at 3-year intervals.^18,19

Combined cytologic and HPV testing has received its strongest endorsement to date from the ACS/ASCCP/ASCP, ACOG, and USPSTF in their latest guidelines.^2–4

In 2003, ACOG gave HPV and cytology combined testing an “optional” recommendation for women over age 30; in 2009, it upgraded its recommendation to the highest level of recommendation.¹ At that time, the USPSTF did not recommend for or against HPV testing, while the ACS did recommend HPV testing (with cytology testing alone every 2 to 3 years as an alternative screening strategy).⁵

Now, the ACS/ASCCP/ASCP and ACOG recommend HPV and cytology combined testing as the preferred strategy for screening women age 30 or over.^2,4 Similarly, the USPSTF gives combined testing for women age 30 to 65 a grade A (its highest) recommendation.³ (In 2003, it had given it a grade I—insufficient evidence to assess the balance of benefit and harm.)

Evidence. Several recent studies provide compelling evidence that HPV testing has high sensitivity and excellent negative predictive value, supporting the stronger endorsement of HPV testing and longer screening intervals.

The Joint European Cohort study,²⁰ in 24,295 women, conclusively showed that the 6-year risk of CIN3+ following a negative HPV test was significantly lower than that following a negative cytology result alone (0.27% vs 0.97%).

Katki et al,²¹ in another retrospective study, analyzed data from 330,000 women age 30 and older who underwent combined HPV and cytology testing. Looking at the tests separately, they found the risk of CIN3+ was comparable in the 3 years following a negative cytology test by itself and in the 5 years following negative combined HPV and cytology testing. In fact, combined testing at 5- or 6-year intervals offered better protection than cytology alone at 3-year intervals.

Furthermore, combined testing is also more sensitive for detecting cervical adenocarcinoma.²² (Most cancers of the cervix are squamous cell carcinomas, but approximately 10% are adenocarcinomas.)

Stop screening sooner

In 2002, the ACS recommended ending screening at age 70,¹¹ and in 2009 ACOG said to stop at age 65 to 70.¹ Now, the ACS/ASCCP/ASCP group² and ACOG⁴ recommend stopping screening sooner—at age 65—provided that:

• The patient has had adequate negative screening until then. (Adequate negative prior screening is defined as three consecutive negative cytology results or two consecutive negative combined HPV and cytologic testing results within the 10 years before ceasing screening, with the most recent test performed within the last 5 years.)
• The patient has no history of CIN2+ within the last 20 years.
• The patient is not at high risk of cervical cancer, eg, no history of a high-grade precancerous cervical lesion or cervical cancer, in utero exposure to diethylstilbestrol, or immunosuppression (eg, HIV infection).

The USPSTF had already adopted this position.

Evidence. In women over age 65 who have had good screening, cervical cancer is rare and CIN2+ is uncommon.^2,23,24 Kulasingam et al,⁹ in a modeling study performed for the USPSTF, calculated that continuing to screen until age 90 prevents only 1.6 cancer cases and 0.5 cancer deaths and extends life expectancy by only 1 year per 1,000 women.

Other studies also suggest that newly acquired high-risk HPV infection in women age 65 or older is associated with a very low absolute risk of HPV persistence and CIN3+ progression.^25,26

In addition, cervical cancer takes a median of 20 to 25 years to develop after infection with high-risk HPV.² Also, continuing to screen this older population will detect only a very small number of new cases of CIN2+ and may lead to harm from overtreatment.

Finally, postmenopausal women often have smaller and less accessible cervical transformation zones that may require more interventions to obtain adequate samples and to treat.

Stop screening after hysterectomy

The ACS/ASCCP/ASCP group, ACOG, and the USPSTF reaffirmed their recommendation against screening in women who have had a hysterectomy with removal of the cervix for a reason other than cancer and who have had no history of CIN2+ or cervical cancer.^2–4

Evidence. Several lines of evidence suggest stopping screening after a woman has a hysterectomy. The incidence of vaginal cancer is extremely low,²⁷ and the positive predictive value of cytologic testing of the vaginal cuff for vaginal cancer was zero in one study.²⁸ Also, a large cross-sectional study of 5,330 screening cytology tests in women who had a hysterectomy found only one case of dysplasia and no cancer.²⁹

Continue to screen after HPV vaccination

For the first time since HPV vaccines were introduced in 2006, the ACS/ASCCP/ASCP, ACOG, and the USPSTF have had to consider what to do for vaccinated women. All of their new guidelines say to keep screening them.

Evidence. The currently available HPV vaccines protect against cervical cancer,³⁰ but only against cervical cancer caused by HPV types 16 and 18. Other oncogenic types of HPV exist, and the current vaccines do not protect against them.

Furthermore, many women are vaccinated who are already infected. In addition, as of 2010, only about 32% of eligible girls and women in the United States had received all three recommended doses of the vaccine.³¹ And modeling studies predict that the impact of the HPV vaccine will not be apparent for at least another decade.³²

HPV 16/18 genotyping

The ACS/ASCCP/ASCP and ACOG now recommend HPV 16/18 genotyping as a triage option in women who have positive results on HPV testing but negative cytology results, and immediate referral for colposcopy if the genotyping test is positive.² The alternative option in this situation is to repeat combined HPV and cytologic testing in 12 months.^2,33

Evidence. The standard tests for HPV can detect DNA from about a dozen of the oncogenic types of HPV depending on the test, but they do not tell you which one the patient has. This information may be relevant, since not all “high-risk” HPV types are equally bad. HPV 16 and HPV 18 are the worst of all, together accounting for more than 70% of cases of cervical cancer.

Large cohort studies^34,35 have shown that the risk of CIN3 reaches 10% over 1 to 4 years in women who test positive for HPV 16, and over 2 to 5 years if they test positive for HPV 18. This clinically relevant short-term risk supports immediate referral for colposcopy.

In March 2009, the US Food and Drug Administration (FDA) approved a test for HPV 16 and HPV 18—Cervista HPV 16/18 (Hologic, Bedford, MA).³⁶

More recently, researchers from the Addressing the Need for Advanced HPV Diagnostics (ATHENA) trial,³⁷ in 47,208 women, reported that they found CIN2+ in 11.4% of women who tested positive for either HPV 16 or HPV 18, and CIN3+ in 9.8%. Of those who were positive for HPV 16, 13.6% had CIN2+ and 11.7% had CIN3+.

WHAT’S COMING?

As we gain knowledge of the molecular oncogenesis of cervical cancer, we appreciate more the complex relation between HPV oncoproteins and cervical dysplasia. Recent studies demonstrated the clinical utility of detecting novel markers in women who have positive HPV results.^38,39

At present, however, there is insufficient evidence to integrate these strategies into our standard of care for cervical cancer screening.

Novel biomarkers: p16 and Ki-67

Although HPV testing is sensitive, it has poor specificity and positive predictive value.^40,41 In a primary screening setting, women with normal cytology results who test positive for high-risk HPV may carry a risk of only 3% to 7% for high-grade CIN.^42,43

HPV 16/18 genotyping can be useful in this situation (see above). However, not everyone who carries HPV 16 or 18 goes on to develop CIN or cancer.⁴⁴

A novel biomarker, p16, has been shown to be overexpressed in cervical dysplasia and associated with high-risk HPV oncogenic transformation. Another novel marker, Ki-67, can be regarded as a surrogate marker of deregulated cell proliferation (Figure 1).³⁸

A recent study reported that a combined test for both of these markers (dual-stained cytology) had a sensitivity of 91.9% for detecting CIN2+ and 96.4% for CIN3+. This test was also highly specific: 82.1% for CIN2+ and 76.9% for CIN3+.³⁸

An Italian randomized trial reported that p16 immunostaining improved the specificity of HPV testing in detecting CIN2+.⁴⁵

In addition, the European Equivocal or Mildly Abnormal Papanicolaou Cytology Study⁴⁶ found that the dual-stained cytology test had excellent sensitivity for CIN2+ in women with atypical squamous cells of undetermined significance (ASCUS) or low-grade squamous intraepithelial lesion (LSIL) cytology results (92.2% for ASCUS, 94.2% for LSIL). The specificity for CIN2+ in ASCUS and LSIL was 80.6% and 68%, respectively.

A US study also showed that the sensitivity and specificity to detect CIN3+ by using p16/Ki-67 were 97.2% and 60%, respectively, in women age 30 and older.⁴⁷

If confirmed in more studies, p16/Ki-67 dual staining could help us in deciding which women who have positive HPV but negative cytology results should be referred for colposcopy.

HPV oncogene E6/E7 mRNA testing

In October 2011, the FDA approved the clinical use of a new-generation HPV test, the Aptima HPV assay (Hologic Gen-Probe, San Diego, CA), which detects mRNA for the proteins E6 and E7 from high-risk HPV.³⁹

HPV E6/E7 mRNA expression has been found in virtually all HPV-positive cancer cases and demonstrates a stronger correlation with cervical disease than detection of HPV DNA.⁴⁸ High-risk HPV E6 and E7 proteins immortalize and malignantly transform infected cells by inhibiting two host cellular anticancer proteins, p53 and retinoblastoma protein (pRB).^44,49

The recent FDA approval was based on data from the CLEAR (Clinical Evaluation of Aptima HPV RNA) trial.³⁹ In this trial, in more than 11,000 women, the test was as sensitive for detecting CIN2+ as the HPV DNA-based test, and it was more specific. This advantage was statistically significant. The higher specificity may reduce the number of unnecessary colposcopies and allow for more effective management.^50,51

A promising future screening strategy: HPV testing first, then cytology

HPV testing is more sensitive than cytology, while cytology is more specific. Thus, it would be logical to test for HPV first, and then to perform cytologic testing in patients who have positive results on HPV testing.

In the past 5 years, several large randomized clinical trials within national screening programs in Italy, England, Sweden, and the Netherlands examined the value of a primary HPV-based screening strategy.^15–17,52 These studies confirmed the superior sensitivity of HPV testing for detection of CIN2+.

A large Canadian randomized trial⁵³ compared HPV testing and cytologic testing as screening tests in women age 30 to 69. HPV DNA testing was 94.6% sensitive in detecting CIN2 or CIN3, compared with 55.4% for cytology. The specificity of HPV testing was nearly as high as that of cytology, 94.1% vs 96.8%. Furthermore, HPV testing followed (in those positive for HPV) by cytology resulted in a lower referral rate for colposcopy than did either test alone (1.1% vs 2.9% with cytology alone or 6.1% with HPV testing alone).

More randomized trial data are needed to evaluate the validity of this promising new approach in varied populations. The HPV FOCAL trial is comparing HPV-then-cytology testing vs cytology-then (in women with ASCUS)-HPV testing.⁵⁴ In addition, the aforementioned novel biomarkers for HPV oncogenic activity may eventually play a greater role in primary screening.

With the latest evidence-based screening guidelines, we can implement a more sensitive and effective screening strategy for better prevention and early detection of cervical cancer. Newer cutting-edge molecular technologies appear promising; however, their cost-effectiveness needs to be further evaluated.

A MORAL AND ETHICAL RESPONSIBILITY

Our unscreened and underscreened populations carry a higher burden of cervical cancer and of death from cervical cancer. Identifying and reaching out to these women is our moral and ethical responsibility and yet poses the biggest challenge in screening. Arguably, this could have the most significant impact on rates of death from cervical cancer.

Innovative measures in overcoming healthcare barriers and in making testing cheaper will help to close the gap between well-screened and underscreened populations in the United States and globally. Examples would be a low-cost, point-of-care screening test for the general population, and a government-subsidized global vaccination program. It is entirely conceivable that women will no longer die from cervical cancer in the near future, thanks to global effective screening and preventive efforts through widespread HPV vaccination.

Advances in our understanding of the pathogenesis of cervical cancer, new tests for human papillomavirus (HPV), and the development of HPV vaccines in the last decade are transforming the way we screen for cervical cancer.

As a result, screening guidelines are evolving rapidly, requiring clinicians to keep up-to-date with the evidence and rationales supporting the latest guidelines to properly convey best practices to patients.^1–3

For example, we must understand why it is safe to extend the screening interval in women at low risk (as recommended in the new guidelines), and we need to be familiar with the options for women who test positive for HPV. Patients and providers may often find such new recommendations frustrating, and patients may feel that they are being denied something necessary by insurers rather than being treated according to scientific evidence.

This article will review the newest screening guidelines and the evidence supporting these recommendations for primary care providers. We will also review the potential role of novel biomarkers, newer HPV tests, and possible future strategies for cervical cancer screening.

WHAT’S NEW IN THE LATEST SCREENING GUIDELINES

Over the years, various organizations have issued separate screening guidelines, sometimes agreeing with each other, sometimes disagreeing.⁴ Now, for the first time, several of these organizations have developed guidelines collaboratively, and we have consensus in the screening recommendations.

Shortly after the American Congress of Obstetricians and Gynecologists (ACOG) issued its screening guidelines in December 2009,¹ the American Cancer Society (ACS), American Society for Colposcopy and Cervical Pathology (ASCCP), and American Society for Clinical Pathology (ASCP) convened an expert panel to review the available evidence and develop a new joint screening guideline. Concurrently, the US Preventive Services Task Force (USPSTF) commissioned a targeted systematic review of the latest evidence.

Both the ACS/ASCCP/ASCP group² and the USPSTF³ released their new guidelines on March 14, 2012. In November 2012, ACOG issued its latest recommendation on cervical cancer screening.⁴ The following discussion highlights the consensus recommendations from these organizations (Table 1).

These guidelines apply to the general population only. They do not apply to women at high risk who may require more intensive screening, such as those who have a history of cervical cancer, are immunocompromised (eg, positive for human immunodeficiency virus [HIV]), or were exposed in utero to diethylstilbestrol.

Start screening at age 21

According to the new guidelines, women younger than 21 years should not be screened, regardless of the age at which they start having sex.^1–3 This is a change from the 2002 and 2003 ACS recommendations, which said screening should begin 3 years after the onset of vaginal intercourse.^5,6

Evidence. The rationale for the recommendation not to screen before age 21 stems from two pieces of evidence:

• Invasive cervical cancer is rare in this age group.⁷
• Screening can cause harm. For example, unnecessary treatment of preinvasive lesions can lead to long-term complications such as cervical stenosis, preterm delivery, and preterm premature rupture of membranes.^8,9

Additionally, one study found that screening before age 21 has little or no impact on the incidence of invasive cervical cancer.¹⁰

Longer screening intervals

The 2012 ACS/ASCCP/ASCP guidelines² and the latest ACOG guidelines⁴ lengthen the interval between cytology (Papanicolaou) testing to every 3 years in women age 21 to 29. Previous recommendations from these groups were to screen every 2 years, and the USPSTF first recommended the 3-year interval in 2003.¹¹

For women age 30 to 65, the ACS/ASCCP/ASCP, ACOG, and the USPSTF now recommend screening every 5 years if the patient’s results on combined cytology and HPV testing are negative. However, cytologic testing alone every 3 years is also acceptable.^2–4

Evidence. The evidence supporting a 3-year screening interval in women age 21 to 29 is primarily from modeling studies—no randomized clinical trial has been done. These studies found no significant difference in outcomes with a 2-year vs a 3-year screening interval.^12,13 In particular, the predicted lifetime risk of cervical cancer in women screened every 3 years was 5 to 8 new cases of cancer per 1,000 women, compared with 4 to 6 cases per 1,000 women screened every 2 years.¹⁴

Similarly, screening women younger than age 30 at 2-year or 3-year intervals carried the same predicted lifetime risk of death from cervical cancer of 0.05 per 1,000 women, yet women screened every 2 years underwent 40% more colposcopies than those screened every 3 years.² Therefore, screening every 3 years offers the best balance of benefits and risks in this age group.

Adding HPV testing to cytologic testing increases the sensitivity of screening—thus the recommendation to lengthen the screening interval to every 5 years in women age 30 to 65 who are at low risk and who have negative results on both tests. (Previously, the interval was 3 years.)

Specifically, adding HPV testing improves the sensitivity of screening for cervical intraepithelial neoplasia grade 3 (CIN3), so that, in subsequent rounds of screening, fewer cases of CIN3 or worse (CIN3+) or cancer are detected.^15–17 The longer diagnostic lead time with combined testing is associated with a lower risk of CIN3+ or cancer following a double-negative test result than screening with cytology alone at shorter intervals. Combined testing at 5-year intervals is associated with a similar or lower cancer risk than cytology-alone screening at 3-year intervals.⁹

Moreover, modeling studies have shown that combined testing of women age 30 and older at 5-year intervals leads to fewer colposcopies and a similar or lower cancer risk than with cytology screening at 3-year intervals.^18,19

Combined cytologic and HPV testing has received its strongest endorsement to date from the ACS/ASCCP/ASCP, ACOG, and USPSTF in their latest guidelines.^2–4

In 2003, ACOG gave HPV and cytology combined testing an “optional” recommendation for women over age 30; in 2009, it upgraded its recommendation to the highest level of recommendation.¹ At that time, the USPSTF did not recommend for or against HPV testing, while the ACS did recommend HPV testing (with cytology testing alone every 2 to 3 years as an alternative screening strategy).⁵

Now, the ACS/ASCCP/ASCP and ACOG recommend HPV and cytology combined testing as the preferred strategy for screening women age 30 or over.^2,4 Similarly, the USPSTF gives combined testing for women age 30 to 65 a grade A (its highest) recommendation.³ (In 2003, it had given it a grade I—insufficient evidence to assess the balance of benefit and harm.)

Evidence. Several recent studies provide compelling evidence that HPV testing has high sensitivity and excellent negative predictive value, supporting the stronger endorsement of HPV testing and longer screening intervals.

The Joint European Cohort study,²⁰ in 24,295 women, conclusively showed that the 6-year risk of CIN3+ following a negative HPV test was significantly lower than that following a negative cytology result alone (0.27% vs 0.97%).

Katki et al,²¹ in another retrospective study, analyzed data from 330,000 women age 30 and older who underwent combined HPV and cytology testing. Looking at the tests separately, they found the risk of CIN3+ was comparable in the 3 years following a negative cytology test by itself and in the 5 years following negative combined HPV and cytology testing. In fact, combined testing at 5- or 6-year intervals offered better protection than cytology alone at 3-year intervals.

Furthermore, combined testing is also more sensitive for detecting cervical adenocarcinoma.²² (Most cancers of the cervix are squamous cell carcinomas, but approximately 10% are adenocarcinomas.)

Stop screening sooner

In 2002, the ACS recommended ending screening at age 70,¹¹ and in 2009 ACOG said to stop at age 65 to 70.¹ Now, the ACS/ASCCP/ASCP group² and ACOG⁴ recommend stopping screening sooner—at age 65—provided that:

• The patient has had adequate negative screening until then. (Adequate negative prior screening is defined as three consecutive negative cytology results or two consecutive negative combined HPV and cytologic testing results within the 10 years before ceasing screening, with the most recent test performed within the last 5 years.)
• The patient has no history of CIN2+ within the last 20 years.
• The patient is not at high risk of cervical cancer, eg, no history of a high-grade precancerous cervical lesion or cervical cancer, in utero exposure to diethylstilbestrol, or immunosuppression (eg, HIV infection).

The USPSTF had already adopted this position.

Evidence. In women over age 65 who have had good screening, cervical cancer is rare and CIN2+ is uncommon.^2,23,24 Kulasingam et al,⁹ in a modeling study performed for the USPSTF, calculated that continuing to screen until age 90 prevents only 1.6 cancer cases and 0.5 cancer deaths and extends life expectancy by only 1 year per 1,000 women.

Other studies also suggest that newly acquired high-risk HPV infection in women age 65 or older is associated with a very low absolute risk of HPV persistence and CIN3+ progression.^25,26

In addition, cervical cancer takes a median of 20 to 25 years to develop after infection with high-risk HPV.² Also, continuing to screen this older population will detect only a very small number of new cases of CIN2+ and may lead to harm from overtreatment.

Finally, postmenopausal women often have smaller and less accessible cervical transformation zones that may require more interventions to obtain adequate samples and to treat.

Stop screening after hysterectomy

The ACS/ASCCP/ASCP group, ACOG, and the USPSTF reaffirmed their recommendation against screening in women who have had a hysterectomy with removal of the cervix for a reason other than cancer and who have had no history of CIN2+ or cervical cancer.^2–4

Evidence. Several lines of evidence suggest stopping screening after a woman has a hysterectomy. The incidence of vaginal cancer is extremely low,²⁷ and the positive predictive value of cytologic testing of the vaginal cuff for vaginal cancer was zero in one study.²⁸ Also, a large cross-sectional study of 5,330 screening cytology tests in women who had a hysterectomy found only one case of dysplasia and no cancer.²⁹

Continue to screen after HPV vaccination

For the first time since HPV vaccines were introduced in 2006, the ACS/ASCCP/ASCP, ACOG, and the USPSTF have had to consider what to do for vaccinated women. All of their new guidelines say to keep screening them.

Evidence. The currently available HPV vaccines protect against cervical cancer,³⁰ but only against cervical cancer caused by HPV types 16 and 18. Other oncogenic types of HPV exist, and the current vaccines do not protect against them.

Furthermore, many women are vaccinated who are already infected. In addition, as of 2010, only about 32% of eligible girls and women in the United States had received all three recommended doses of the vaccine.³¹ And modeling studies predict that the impact of the HPV vaccine will not be apparent for at least another decade.³²

HPV 16/18 genotyping

The ACS/ASCCP/ASCP and ACOG now recommend HPV 16/18 genotyping as a triage option in women who have positive results on HPV testing but negative cytology results, and immediate referral for colposcopy if the genotyping test is positive.² The alternative option in this situation is to repeat combined HPV and cytologic testing in 12 months.^2,33

Evidence. The standard tests for HPV can detect DNA from about a dozen of the oncogenic types of HPV depending on the test, but they do not tell you which one the patient has. This information may be relevant, since not all “high-risk” HPV types are equally bad. HPV 16 and HPV 18 are the worst of all, together accounting for more than 70% of cases of cervical cancer.

Large cohort studies^34,35 have shown that the risk of CIN3 reaches 10% over 1 to 4 years in women who test positive for HPV 16, and over 2 to 5 years if they test positive for HPV 18. This clinically relevant short-term risk supports immediate referral for colposcopy.

In March 2009, the US Food and Drug Administration (FDA) approved a test for HPV 16 and HPV 18—Cervista HPV 16/18 (Hologic, Bedford, MA).³⁶

More recently, researchers from the Addressing the Need for Advanced HPV Diagnostics (ATHENA) trial,³⁷ in 47,208 women, reported that they found CIN2+ in 11.4% of women who tested positive for either HPV 16 or HPV 18, and CIN3+ in 9.8%. Of those who were positive for HPV 16, 13.6% had CIN2+ and 11.7% had CIN3+.

WHAT’S COMING?

As we gain knowledge of the molecular oncogenesis of cervical cancer, we appreciate more the complex relation between HPV oncoproteins and cervical dysplasia. Recent studies demonstrated the clinical utility of detecting novel markers in women who have positive HPV results.^38,39

At present, however, there is insufficient evidence to integrate these strategies into our standard of care for cervical cancer screening.

Novel biomarkers: p16 and Ki-67

Although HPV testing is sensitive, it has poor specificity and positive predictive value.^40,41 In a primary screening setting, women with normal cytology results who test positive for high-risk HPV may carry a risk of only 3% to 7% for high-grade CIN.^42,43

HPV 16/18 genotyping can be useful in this situation (see above). However, not everyone who carries HPV 16 or 18 goes on to develop CIN or cancer.⁴⁴

A novel biomarker, p16, has been shown to be overexpressed in cervical dysplasia and associated with high-risk HPV oncogenic transformation. Another novel marker, Ki-67, can be regarded as a surrogate marker of deregulated cell proliferation (Figure 1).³⁸

A recent study reported that a combined test for both of these markers (dual-stained cytology) had a sensitivity of 91.9% for detecting CIN2+ and 96.4% for CIN3+. This test was also highly specific: 82.1% for CIN2+ and 76.9% for CIN3+.³⁸

An Italian randomized trial reported that p16 immunostaining improved the specificity of HPV testing in detecting CIN2+.⁴⁵

In addition, the European Equivocal or Mildly Abnormal Papanicolaou Cytology Study⁴⁶ found that the dual-stained cytology test had excellent sensitivity for CIN2+ in women with atypical squamous cells of undetermined significance (ASCUS) or low-grade squamous intraepithelial lesion (LSIL) cytology results (92.2% for ASCUS, 94.2% for LSIL). The specificity for CIN2+ in ASCUS and LSIL was 80.6% and 68%, respectively.

A US study also showed that the sensitivity and specificity to detect CIN3+ by using p16/Ki-67 were 97.2% and 60%, respectively, in women age 30 and older.⁴⁷

If confirmed in more studies, p16/Ki-67 dual staining could help us in deciding which women who have positive HPV but negative cytology results should be referred for colposcopy.

HPV oncogene E6/E7 mRNA testing

In October 2011, the FDA approved the clinical use of a new-generation HPV test, the Aptima HPV assay (Hologic Gen-Probe, San Diego, CA), which detects mRNA for the proteins E6 and E7 from high-risk HPV.³⁹

HPV E6/E7 mRNA expression has been found in virtually all HPV-positive cancer cases and demonstrates a stronger correlation with cervical disease than detection of HPV DNA.⁴⁸ High-risk HPV E6 and E7 proteins immortalize and malignantly transform infected cells by inhibiting two host cellular anticancer proteins, p53 and retinoblastoma protein (pRB).^44,49

The recent FDA approval was based on data from the CLEAR (Clinical Evaluation of Aptima HPV RNA) trial.³⁹ In this trial, in more than 11,000 women, the test was as sensitive for detecting CIN2+ as the HPV DNA-based test, and it was more specific. This advantage was statistically significant. The higher specificity may reduce the number of unnecessary colposcopies and allow for more effective management.^50,51

A promising future screening strategy: HPV testing first, then cytology

HPV testing is more sensitive than cytology, while cytology is more specific. Thus, it would be logical to test for HPV first, and then to perform cytologic testing in patients who have positive results on HPV testing.

In the past 5 years, several large randomized clinical trials within national screening programs in Italy, England, Sweden, and the Netherlands examined the value of a primary HPV-based screening strategy.^15–17,52 These studies confirmed the superior sensitivity of HPV testing for detection of CIN2+.

A large Canadian randomized trial⁵³ compared HPV testing and cytologic testing as screening tests in women age 30 to 69. HPV DNA testing was 94.6% sensitive in detecting CIN2 or CIN3, compared with 55.4% for cytology. The specificity of HPV testing was nearly as high as that of cytology, 94.1% vs 96.8%. Furthermore, HPV testing followed (in those positive for HPV) by cytology resulted in a lower referral rate for colposcopy than did either test alone (1.1% vs 2.9% with cytology alone or 6.1% with HPV testing alone).

More randomized trial data are needed to evaluate the validity of this promising new approach in varied populations. The HPV FOCAL trial is comparing HPV-then-cytology testing vs cytology-then (in women with ASCUS)-HPV testing.⁵⁴ In addition, the aforementioned novel biomarkers for HPV oncogenic activity may eventually play a greater role in primary screening.

With the latest evidence-based screening guidelines, we can implement a more sensitive and effective screening strategy for better prevention and early detection of cervical cancer. Newer cutting-edge molecular technologies appear promising; however, their cost-effectiveness needs to be further evaluated.

A MORAL AND ETHICAL RESPONSIBILITY

Our unscreened and underscreened populations carry a higher burden of cervical cancer and of death from cervical cancer. Identifying and reaching out to these women is our moral and ethical responsibility and yet poses the biggest challenge in screening. Arguably, this could have the most significant impact on rates of death from cervical cancer.

Innovative measures in overcoming healthcare barriers and in making testing cheaper will help to close the gap between well-screened and underscreened populations in the United States and globally. Examples would be a low-cost, point-of-care screening test for the general population, and a government-subsidized global vaccination program. It is entirely conceivable that women will no longer die from cervical cancer in the near future, thanks to global effective screening and preventive efforts through widespread HPV vaccination.

The vaccines against human papillomavirus (HPV) are the only ones designed to prevent cancer caused by a virus^1,2—surely a good goal. But because HPV is sexually transmitted, HPV vaccination has met with public controversy.³ To counter the objections and better protect their patients’ health, primary care providers and other clinicians need a clear understanding of the benefits and the low risk of HPV vaccination—and the reasons so many people object to it.³

In this article, we will review:

• The impact of HPV-related diseases
• The basic biologic features of HPV vaccines
• The host immune response to natural HPV infection vs the response to HPV vaccines
• The clinical efficacy and safety of HPV vaccines
• The latest guidelines for HPV vaccination
• The challenges to vaccination implementation
• Frequently asked practical questions about HPV vaccination.

HPV-RELATED DISEASES: FROM BOTHERSOME TO DEADLY

Clinical sequelae of HPV infection include genital warts; cancers of the cervix, vulva, vagina, anus, penis, and oropharynx; and recurrent respiratory papillomatosis.^4–6

Genital warts

HPV types 6 and 11 are responsible for more than 90% of the 1 million new cases of genital warts diagnosed annually in the United States.^7–10

Bothersome and embarrassing, HPV-related genital warts can cause itching, burning, erythema, and pain, as well as epithelial erosions, ulcerations, depigmentation, and urethral and vaginal bleeding and discharge.^11,12 Although they are benign in the oncologic sense, they can cause a good deal of emotional and financial stress. Patients may feel anxiety, embarrassment,¹³ and vulnerability. Adolescents and adults who have or have had genital warts need to inform their current and future partners or else risk infecting them—and facing the consequences.

Direct health care costs of genital warts in the United States have been estimated to be at least $200 million per year.¹⁴

Cervical cancer

Cervical cancer cannot develop unless the cervical epithelium is infected with one of the oncogenic HPV types. Indeed, oncogenic HPV is present in as many as 99.8% of cervical cancer specimens.¹⁵ HPV 16 and 18 are the most oncogenic HPV genotypes and account for 75% of all cases of cervical cancer. Ten other HPV genotypes account for the remaining 25%.¹⁶

In 2012, there were an estimated 12,170 new cases of invasive cervical cancer in the United States and 4,220 related deaths.¹⁷ The cost associated with cervical cancer screening, managing abnormal findings, and treating invasive cervical cancer in the United States is estimated to be $3.3 billion per year.¹⁸

Although the incidence and the mortality rates of cervical cancer have decreased more than 50% in the United States over the past 3 decades thanks to screening,¹⁹ cervical cancer remains the second leading cause of death from cancer in women worldwide. Each year, an estimated 500,000 women contract the disease and 240,000 die of it.²⁰

Anal cancer

A recent study indicated that oncogenic HPV can also cause anal cancer, and the proportion of such cancers associated with HPV 16 or HPV 18 infection is as high as or higher than for cervical cancers, and estimated at 80%.²¹

The incidence of anal cancer is increasing by approximately 2% per year in both men and women in the general population,²² and rates are even higher in men who have sex with men and people infected with the human immunodeficiency virus.²³

Hu and Goldie²⁴ estimated that the lifetime costs of caring for all the people in the United States who in just 1 year (2003) acquired anal cancer attributable to HPV would total $92 million.

Oropharyngeal cancer

HPV types 16, 18, 31, 33, and 35 also cause oropharyngeal cancer. HPV 16 accounts for more than 90% of cases of HPV-related oropharyngeal cancer.²⁵

Chaturvedi et al⁶ tested tissue samples from three national cancer registries and found that the number of oropharyngeal cancers that were HPV-positive increased from 16.3% in 1984–1989 to 71.7% in 2000–2004, while the number of HPV-negative oropharyngeal cancers fell by 50%, paralleling the drop in cigarette smoking in the United States.

Hu and Goldie²⁴ estimated that the total lifetime cost for all new HPV-related oropharyngeal cancers that arose in 2003 would come to $38.1 million.²⁴

Vulvar and vaginal cancers

HPV 16 and 18 are also responsible for approximately 50% of vulvar cancers and 50% to 75% of vaginal cancers.^4,5

Recurrent respiratory papillomatosis

HPV 6 and 11 cause almost all cases of juvenile- and adult-onset recurrent respiratory papillomatosis.²⁶ The annual cost for surgical procedures for this condition in the United States has been estimated at $151 million.²⁷

HPV VACCINES ARE NONINFECTIOUS AND NONCARCINOGENIC

Currently, two HPV vaccines are available: a quadrivalent vaccine against types 6, 11, 16, and 18 (Gardasil; Merck) and a bivalent vaccine against types 16 and 18 (Cervarix; Glaxo-SmithKline). The quadrivalent vaccine was approved by the US Food and Drug Administration (FDA) in 2006, and the bivalent vaccine was approved in 2009.^28,29

Both vaccines contain virus-like particles, ie, viral capsids that contain no DNA. HPV has a circular DNA genome of 8,000 nucleotides divided into two regions: the early region, for viral replication, and the late region, for viral capsid production. The host produces neutralizing antibodies in response to the L1 capsid protein, which is different in different HPV types.

In manufacturing the vaccines, the viral L1 gene is incorporated into a yeast genome or an insect virus genome using recombinant DNA technology (Figure 1). Grown in culture, the yeast or the insect cells produce the HPV L1 major capsid protein, which has the intrinsic capacity to self-assemble into virus-like particles.^30–33 These particles are subsequently purified for use in the vaccines.³⁴

Recombinant virus-like particles are morphologically indistinguishable from authentic HPV virions and contain the same typespecific antigens present in authentic virions. Therefore, they are highly effective in inducing a host humoral immune response. And because they do not contain HPV DNA, the recombinant HPV vaccines are noninfectious and noncarcinogenic.³⁵

VACCINATION INDUCES A STRONGER IMMUNE RESPONSE THAN INFECTION

HPV infections trigger both a humoral and a cellular response in the host immune system.

The humoral immune response to HPV infection involves producing neutralizing antibody against the specific HPV type, specifically the specific L1 major capsid protein. This process is typically somewhat slow and weak, and only about 60% of women with a new HPV infection develop antibodies to it.^36,37

HPV has several ways to evade the host immune system. It does not infect or replicate within the antigen-presenting cells in the epithelium. In addition, HPV-infected keratinocytes are less susceptible to cytotoxic lymphocytic-mediated lysis. Moreover, HPV infection cause very little tissue destruction. And finally, natural cervical HPV infection does not result in viremia. As a result, antigen-presenting cells have no chance to engulf the virions and present virion-derived antigen to the host immune system. The immune system outside the epithelium has limited opportunity to detect the virus because HPV infection does not have a blood-borne phase.^38,39

The cell-mediated immune response to early HPV oncoproteins may help eliminate established HPV infection.⁴⁰ In contrast to antibodies, the T-cell response to HPV has not been shown to be specific to HPV type.⁴¹ Clinically, cervical HPV infection is common, but most lesions go into remission or resolve as a result of the cell-mediated immune response.^40,41

In contrast to the weak, somewhat ineffective immune response to natural HPV infection, the antibody response to HPV vaccines is rather robust. In randomized controlled trials, almost all vaccinated people have seroconverted. The peak antibody concentrations are 50 to 10,000 times greater than in natural infection. Furthermore, the neutralizing antibodies induced by HPV vaccines persist for as long as 7 to 9 years after immunization.⁴² However, the protection provided by HPV vaccines against HPV-related cervical intraepithelial neoplasia does not necessarily correlate with the antibody concentration.^43–47

Why does the vaccine work so well?

Why are vaccine-induced antibody responses so much stronger than those induced by natural HPV infection?

The first reason is that the vaccine, delivered intramuscularly, rapidly enters into blood vessels and the lymphatic system. In contrast, in natural intraepithelial infection, the virus is shed from mucosal surfaces and does not result in viremia.⁴⁸

In addition, the strong immunogenic nature of the virus-like particles induces a robust host antibody response even in the absence of adjuvant because of concentrated neutralizing epitopes and excellent induction of the T-helper cell response.^35,49,50

The neutralizing antibody to L1 prevents HPV infection by blocking HPV from binding to the basement membrane as well as to the epithelial cell receptor during epithelial microabrasion and viral entry. The subsequent micro-wound healing leads to serous exudation and rapid access of serum immunoglobulin G (IgG) to HPV virus particles and encounters with circulatory B memory cells.

Furthermore, emerging evidence suggests that even very low antibody concentrations are sufficient to prevent viral entry into cervical epithelial cells.^{46–48,51–53}

THE HPV VACCINES ARE HIGHLY EFFECTIVE AND SAFE

The efficacy and safety of the quadrivalent and the bivalent HPV vaccines have been evaluated in large randomized clinical trials.^{23,28,29,54,55} Table 1 summarizes the key findings.

The Females United to Unilaterally Reduce Endo/ectocervical Disease (FUTURE I)⁵⁴ and FUTURE II²⁸ trials showed conclusively that the quadrivalent HPV vaccine is 98% to 100% efficacious in preventing HPV 16- and 18-related cervical intraepithelial neoplasia, carcinoma in situ, and invasive cervical cancer in women who had not been infected with HPV before. Similarly, the Papilloma Trial against Cancer in Young Adults (PATRICIA) concluded that the bivalent HPV vaccine is 93% efficacious.²⁹

Giuliano et al⁵⁵ and Palefsky et al²³ conducted randomized clinical trials of the quadrivalent HPV vaccine for preventing genital disease and anal intraepithelial neoplasia in boys and men; the efficacy rates were 90.4%⁵⁵ and 77.5%.²³

A recent Finnish trial in boys age 10 to 18 found 100% seroconversion rates for HPV 16 and HPV 18 antibodies after they received bivalent HPV vaccine.⁵⁶ Similar efficacy has been demonstrated for the quadrivalent HPV vaccine in boys.⁵⁷

Adverse events after vaccination

After the FDA approved the quadrivalent HPV vaccine for girls in 2006, the US Centers for Disease Control and Prevention (CDC) conducted a thorough survey of adverse events after immunization from June 1, 2006 through December 31, 2008.⁵⁸ There were about 54 reports of adverse events per 100,000 distributed vaccine doses, similar to rates for other vaccines. However, the incidence rates of syncope and venous thrombosis were disproportionately higher, according to data from the US Vaccine Adverse Event Reporting System. The rate of syncope was 8.2 per 100,000 vaccine doses, and the rate of venous thrombotic events was 0.2 per 100,000 doses.⁵⁸

There were 32 reports of deaths after HPV vaccination, but these were without clear causation. Hence, this information must be interpreted with caution and should not be used to infer causal associations between HPV vaccines and adverse outcomes. The causes of death included diabetic ketoacidosis, pulmonary embolism, prescription drug abuse, amyotrophic lateral sclerosis, meningoencephalitis, influenza B viral sepsis, arrhythmia, myocarditis, and idiopathic seizure disorder.⁵⁸

Furthermore, it is important to note that vasovagal syncope and venous thromboembolic events are more common in young females in general.⁵⁹ For example, the background rates of venous thromboembolism in females age 14 to 29 using oral contraceptives is 21 to 31 per 100,000 woman-years.⁶⁰

Overall, the quadrivalent HPV vaccine is well tolerated and clinically safe. Postlicensure evaluation found that the quadrivalent and bivalent HPV vaccines had similar safety profiles.⁶¹

Vaccination is contraindicated in people with known hypersensitivity or prior severe allergic reactions to vaccine or yeast or who have bleeding disorders.

HPV VACCINATION DOES MORE THAN PREVENT CERVICAL CANCER IN FEMALES

The quadrivalent HPV vaccine was licensed by the FDA in 2006 for use in females age 9 to 26 to prevent cervical cancer, cervical cancer precursors, vaginal and vulval cancer precursors, and anogenital warts caused by HPV types 6, 11, 16, and 18. The CDC’s Advisory Committee on Immunization Practices (ACIP) issued its recommendation for initiating HPV vaccination for females age 11 to 12 in March 2007. The ACIP stated that the vaccine could be given to girls as early as age 9 and recommended catch-up vaccinations for those age 13 to 26.^62,63

The quadrivalent HPV vaccine was licensed by the FDA in 2009 for use in boys and men for the prevention of genital warts. In December 2010, the quadrivalent HPV vaccine received extended licensure from the FDA for use in males and females for the prevention of anal cancer. In October 2011, the ACIP voted to recommend routine use of the quadrivalent HPV vaccine for boys age 11 to 12; catch-up vaccination should occur for those age 13 to 22, with an option to vaccinate men age 23 to 26.

These recommendations replace the “permissive use” recommendations from the ACIP in October 2009 that said the quadrivalent HPV vaccine may be given to males age 9 to 26.⁶⁴ This shift from a permissive to an active recommendation connotes a positive change reflecting recognition of rising oropharyngeal cancer rates attributable to oncogenic, preventable HPV, rising HPV-related anal cancer incidence, and the burden of the disease in female partners of infected men, with associated rising health care costs.

The bivalent HPV vaccine received FDA licensure in October 2009 for use in females age 10 to 25 to prevent cervical cancer and precursor lesions. The ACIP included the bivalent HPV vaccine in its updated recommendations in May 2010 for use in girls age 11 to 12. Numerous national and international organizations have endorsed HPV vaccination.^65–71

Table 2 outlines the recommendations from these organizations.

HPV VACCINATION RATES ARE STILL LOW

HPV vaccine offers us the hope of eventually eradicating cervical cancer. However, the immunization program still faces many challenges, since HPV vaccination touches on issues related to adolescent sexuality, parental autonomy, and cost. As a result, HPV immunization rates remain relatively low in the United States according to several national surveys. Only 40% to 49% of girls eligible for the vaccine received even one dose, and of those who received even one dose, only 32% to 53.3% came back for all three doses.^72–75 Furthermore, indigent and minority teens were less likely to finish the three-dose HPV vaccine series.

Why are the vaccination rates so low?

Parental barriers. In one survey,⁷³ reasons that parents gave for not having their daughters vaccinated included:

• Lack of knowledge of the vaccine (19.4%)
• Lack of perceived need for the vaccine (18.8%)
• Belief that their daughter was not sexually active (18.3%)
• Clinician not recommending vaccination (13.1%).

In an effort to improve HPV vaccination rates,⁴¹ several states proposed legislation for mandatory HPV vaccination of schoolgirls shortly after licensure of the quadrivalent HPV vaccine.³ Since then, we have seen a wave of public opposition rooted in concerns and misinformation about safety, teenage sexuality, governmental coercion, and cost. Widespread media coverage has also highlighted unsubstantiated claims about side effects attributable to the vaccine that can raise parents’ mistrust of vaccines.⁷⁶ Concerns have also been raised about a threat to parental autonomy in how and when to educate their children about sex.⁷⁷

Moreover, the vaccine has raised ethical concerns in some parents and politicians that mandatory vaccination could undermine abstinence messages in sexual education and may alter sexual activity by condoning risky behavior.⁷⁸ However, a recent study indicated that there is no significant change in sexual behavior related to HPV vaccination in young girls.⁷⁹

In 2012, Mullins et al⁸⁰ also found that an urban population of adolescent girls (76.4% black, 57.5% sexually experienced) did not feel they could forgo safer sexual practices after first HPV vaccination, although the girls did perceive less risk from HPV than from other sexually transmitted infections after HPV vaccination (P < .001).⁸⁰ Inadequate knowledge about HPV-related disease and HPV vaccine correlated with less perceived risk from HPV after vaccination among the girls, and a lack of knowledge about HPV and less communication with their daughters about HPV correlated with less perceived risk from HPV in the mothers of the study population.⁸¹

Health-care-provider barriers. Physician endorsement of vaccines represents a key predictor of vaccine acceptance by patients, families, and other clinicians.^82–84 In 2008, a cross-sectional, Internet-based survey of 1,122 Texas pediatricians, family practice physicians, obstetricians, gynecologists, and internal medicine physicians providing direct patient care found that only 48.5% always recommended HPV vaccination to girls.⁷⁴ Of all respondents, 68.4% were likely to recommend the vaccine to boys, and 41.7% agreed with mandated vaccination. Thus, more than half of the physicians were not following the current recommendations for universal HPV vaccination for 11- to -12-year-olds.

In a survey of 1,013 physicians during the spring and summer of 2009, only 34.6% said they always recommend HPV vaccination to early adolescents, 52.7% to middle adolescents, and 50.2% to late adolescents and young adults.⁸⁵ Pediatricians were more likely than family physicians and obstetrician-gynecologists to always recommend HPV vaccine across all age groups (P < .001). Educational interventions targeting various specialties may help overcome physician-related barriers to immunization.⁸⁵

Financial barriers. HPV vaccine, which must be given in three doses, is more expensive than other vaccines, and this expense is yet another barrier, especially for the uninsured.⁸⁶ Australia launched a government-funded program of HPV vaccination (with the quadrivalent vaccine) in schools in 2007, and it has been very successful. Garland et al⁸⁷ reported that new cases of genital warts have decreased by 73% since the program began, and the rate of high-grade abnormalities on Papanicolaou testing has declined by a small but significant amount.

For HPV vaccination to have an impact on public health, vaccination rates in the general population need to be high. In order to achieve these rates, we need to educate our patients on vaccine safety and efficacy and counsel vaccine recipients about the prevention of sexually transmitted infections and the importance of regular cervical cancer screening after age 21. Clinicians can actively “myth-bust” with patients, who may not realize that the vaccine should be given despite a history of HPV infection or abnormal Pap smear.

FREQUENTLY ASKED QUESTIONS

What if the patient is late for a shot?

The current recommended vaccination schedule for the bivalent and quadrivalent HPV vaccines is a three-dose series administered at 0, 2, and 6 months, given as an intramuscular injection, preferably in the deltoid muscle. The minimal dosing interval is 4 weeks between the first and second doses and 12 weeks between the second and third doses.

The vaccines use different adjuncts with different specific mechanisms for immunogenicity; therefore, it is recommended that the same vaccine be used for the entire three-dose series. However, if circumstances preclude the completion of a series with the same vaccine, the other HPV vaccine may be used.⁶³ Starting the series over is not recommended.

Long-term studies demonstrated clinical efficacy 8.5 years after vaccination.⁴⁷ Amnestic response by virtue of activation of pools of memory B cells has been demonstrated, suggesting the vaccine may afford lifelong immunity.⁸⁸

Is a pregnancy test needed before HPV vaccination?

The ACIP states that pregnancy testing is not required before receiving either of the available HPV vaccines.

A recent retrospective review of phase III efficacy trials and pregnancy registry surveillance data for both vaccines revealed no increase in spontaneous abortions, fetal malformations, or adverse pregnancy outcomes.⁸⁹ Data are limited on bivalent and quadrivalent HPV vaccine given within 30 days of pregnancy and subsequent pregnancy and fetal outcomes. Both vaccines have been assigned a pregnancy rating of category B; however, the ACIP recommends that neither vaccine be given if the recipient is known to be pregnant. If pregnancy occurs, it is recommended that the remainder of the series be deferred until after delivery.⁶²

It is not known whether the vaccine is excreted in breast milk. The manufacturers of both the bivalent and quadrivalent HPV vaccines recommend caution when vaccinating lactating women.^30,31

Can HPV vaccine be given with other vaccines?

In randomized trials, giving the bivalent HPV vaccine with the combined hepatitis A, hepatitis B, meningococcal conjugate and the combined tetanus, diphtheria, and acellular pertussis vaccines did not interfere with the immunogenic response, was safe, and was well tolerated.^90,91 Coadministration of the quadrivalent HPV vaccine has been studied only with hepatitis B vaccine, with similar safety and efficacy noted.

The ACIP recommends giving HPV vaccine at the same visit with other age-appropriate immunizations to increase the likelihood of adherence to recommended vaccination schedules.⁶²

Is HPV vaccination cost-effective?

Kim and Goldie⁸⁶ performed a cost-effectiveness analysis of HPV vaccination of girls at age 12 and catch-up vaccination up to the ages of 18, 21, and 26. For their analysis, they considered prevention of cancers associated with HPV types 16 and 18, of genital warts associated with types 6 and 11, and of recurrent respiratory papillomatosis. They also assumed that immunity would be lifelong, and current screening practices would continue.

They calculated that routine vaccination of 12-year-old girls resulted in an incremental cost-effective ratio of $34,900 per quality-adjusted life-year (QALY) gained. A threshold of less than $50,000 per QALY gained is considered reasonably cost-effective, with an upper limit of $100,000 considered acceptable.⁹²

In the same analysis by Kim and Goldie,⁸⁶ catch-up vaccination of girls through age 18 resulted in a cost of $50,000 to $100,000 per QALY gained, and catch-up vaccination of females through age 26 was significantly less cost-effective at more then $130,000 per QALY gained. The vaccine was also significantly less cost-effective if 5% of the population was neither screened nor vaccinated, if a 10-year booster was required, and if frequent cervical cancer screening intervals were adopted.

This analysis did not include costs related to the evaluation and treatment of abnormal Pap smears and cross-protection against other HPV-related cancers.

The cost-effectiveness of HPV vaccination depends on reaching more girls at younger ages (ideally before sexual debut) and completing the three-dose schedule to optimize duration of immunity.⁹² Appropriate modification of the current recommendations for the intervals of cervical cancer screening for vaccinated individuals will further improve the cost-effectiveness of vaccination. The inclusion of male vaccination generally has more favorable cost per QALY in scenarios in which female coverage rates are less than 50%⁹³ and among men who have sex with men.⁹⁴

TO ERADICATE CERVICAL CANCER

Given the remarkable efficacy and expected long-term immunogenicity of HPV vaccines, we anticipate a decline in HPV-related cervical cancer and other related diseases in the years to come. However, modeling studies predicting the impact of HPV vaccination suggest that although substantial reductions in diseases can be expected, the benefit, assuming high vaccination rates, will not be apparent for at least another decade.⁹⁵ Furthermore, the current HPV vaccines contain only HPV 16 and 18 L1 protein for cancer protection and, therefore, do not provide optimal protection against all oncogenic HPV-related cancers.

The real hope of eradicating cervical cancer and all HPV-related disease relies on a successful global implementation of multivalent HPV vaccination, effective screening strategies, and successful treatment.

The vaccines against human papillomavirus (HPV) are the only ones designed to prevent cancer caused by a virus^1,2—surely a good goal. But because HPV is sexually transmitted, HPV vaccination has met with public controversy.³ To counter the objections and better protect their patients’ health, primary care providers and other clinicians need a clear understanding of the benefits and the low risk of HPV vaccination—and the reasons so many people object to it.³

In this article, we will review:

• The impact of HPV-related diseases
• The basic biologic features of HPV vaccines
• The host immune response to natural HPV infection vs the response to HPV vaccines
• The clinical efficacy and safety of HPV vaccines
• The latest guidelines for HPV vaccination
• The challenges to vaccination implementation
• Frequently asked practical questions about HPV vaccination.

HPV-RELATED DISEASES: FROM BOTHERSOME TO DEADLY

Clinical sequelae of HPV infection include genital warts; cancers of the cervix, vulva, vagina, anus, penis, and oropharynx; and recurrent respiratory papillomatosis.^4–6

Genital warts

HPV types 6 and 11 are responsible for more than 90% of the 1 million new cases of genital warts diagnosed annually in the United States.^7–10

Bothersome and embarrassing, HPV-related genital warts can cause itching, burning, erythema, and pain, as well as epithelial erosions, ulcerations, depigmentation, and urethral and vaginal bleeding and discharge.^11,12 Although they are benign in the oncologic sense, they can cause a good deal of emotional and financial stress. Patients may feel anxiety, embarrassment,¹³ and vulnerability. Adolescents and adults who have or have had genital warts need to inform their current and future partners or else risk infecting them—and facing the consequences.

Direct health care costs of genital warts in the United States have been estimated to be at least $200 million per year.¹⁴

Cervical cancer

Cervical cancer cannot develop unless the cervical epithelium is infected with one of the oncogenic HPV types. Indeed, oncogenic HPV is present in as many as 99.8% of cervical cancer specimens.¹⁵ HPV 16 and 18 are the most oncogenic HPV genotypes and account for 75% of all cases of cervical cancer. Ten other HPV genotypes account for the remaining 25%.¹⁶

In 2012, there were an estimated 12,170 new cases of invasive cervical cancer in the United States and 4,220 related deaths.¹⁷ The cost associated with cervical cancer screening, managing abnormal findings, and treating invasive cervical cancer in the United States is estimated to be $3.3 billion per year.¹⁸

Although the incidence and the mortality rates of cervical cancer have decreased more than 50% in the United States over the past 3 decades thanks to screening,¹⁹ cervical cancer remains the second leading cause of death from cancer in women worldwide. Each year, an estimated 500,000 women contract the disease and 240,000 die of it.²⁰

Anal cancer

A recent study indicated that oncogenic HPV can also cause anal cancer, and the proportion of such cancers associated with HPV 16 or HPV 18 infection is as high as or higher than for cervical cancers, and estimated at 80%.²¹

The incidence of anal cancer is increasing by approximately 2% per year in both men and women in the general population,²² and rates are even higher in men who have sex with men and people infected with the human immunodeficiency virus.²³

Hu and Goldie²⁴ estimated that the lifetime costs of caring for all the people in the United States who in just 1 year (2003) acquired anal cancer attributable to HPV would total $92 million.

Oropharyngeal cancer

HPV types 16, 18, 31, 33, and 35 also cause oropharyngeal cancer. HPV 16 accounts for more than 90% of cases of HPV-related oropharyngeal cancer.²⁵

Chaturvedi et al⁶ tested tissue samples from three national cancer registries and found that the number of oropharyngeal cancers that were HPV-positive increased from 16.3% in 1984–1989 to 71.7% in 2000–2004, while the number of HPV-negative oropharyngeal cancers fell by 50%, paralleling the drop in cigarette smoking in the United States.

Hu and Goldie²⁴ estimated that the total lifetime cost for all new HPV-related oropharyngeal cancers that arose in 2003 would come to $38.1 million.²⁴

Vulvar and vaginal cancers

HPV 16 and 18 are also responsible for approximately 50% of vulvar cancers and 50% to 75% of vaginal cancers.^4,5

Recurrent respiratory papillomatosis

HPV 6 and 11 cause almost all cases of juvenile- and adult-onset recurrent respiratory papillomatosis.²⁶ The annual cost for surgical procedures for this condition in the United States has been estimated at $151 million.²⁷

HPV VACCINES ARE NONINFECTIOUS AND NONCARCINOGENIC

Currently, two HPV vaccines are available: a quadrivalent vaccine against types 6, 11, 16, and 18 (Gardasil; Merck) and a bivalent vaccine against types 16 and 18 (Cervarix; Glaxo-SmithKline). The quadrivalent vaccine was approved by the US Food and Drug Administration (FDA) in 2006, and the bivalent vaccine was approved in 2009.^28,29

Both vaccines contain virus-like particles, ie, viral capsids that contain no DNA. HPV has a circular DNA genome of 8,000 nucleotides divided into two regions: the early region, for viral replication, and the late region, for viral capsid production. The host produces neutralizing antibodies in response to the L1 capsid protein, which is different in different HPV types.

In manufacturing the vaccines, the viral L1 gene is incorporated into a yeast genome or an insect virus genome using recombinant DNA technology (Figure 1). Grown in culture, the yeast or the insect cells produce the HPV L1 major capsid protein, which has the intrinsic capacity to self-assemble into virus-like particles.^30–33 These particles are subsequently purified for use in the vaccines.³⁴

Recombinant virus-like particles are morphologically indistinguishable from authentic HPV virions and contain the same typespecific antigens present in authentic virions. Therefore, they are highly effective in inducing a host humoral immune response. And because they do not contain HPV DNA, the recombinant HPV vaccines are noninfectious and noncarcinogenic.³⁵

VACCINATION INDUCES A STRONGER IMMUNE RESPONSE THAN INFECTION

HPV infections trigger both a humoral and a cellular response in the host immune system.

The humoral immune response to HPV infection involves producing neutralizing antibody against the specific HPV type, specifically the specific L1 major capsid protein. This process is typically somewhat slow and weak, and only about 60% of women with a new HPV infection develop antibodies to it.^36,37

HPV has several ways to evade the host immune system. It does not infect or replicate within the antigen-presenting cells in the epithelium. In addition, HPV-infected keratinocytes are less susceptible to cytotoxic lymphocytic-mediated lysis. Moreover, HPV infection cause very little tissue destruction. And finally, natural cervical HPV infection does not result in viremia. As a result, antigen-presenting cells have no chance to engulf the virions and present virion-derived antigen to the host immune system. The immune system outside the epithelium has limited opportunity to detect the virus because HPV infection does not have a blood-borne phase.^38,39

The cell-mediated immune response to early HPV oncoproteins may help eliminate established HPV infection.⁴⁰ In contrast to antibodies, the T-cell response to HPV has not been shown to be specific to HPV type.⁴¹ Clinically, cervical HPV infection is common, but most lesions go into remission or resolve as a result of the cell-mediated immune response.^40,41

In contrast to the weak, somewhat ineffective immune response to natural HPV infection, the antibody response to HPV vaccines is rather robust. In randomized controlled trials, almost all vaccinated people have seroconverted. The peak antibody concentrations are 50 to 10,000 times greater than in natural infection. Furthermore, the neutralizing antibodies induced by HPV vaccines persist for as long as 7 to 9 years after immunization.⁴² However, the protection provided by HPV vaccines against HPV-related cervical intraepithelial neoplasia does not necessarily correlate with the antibody concentration.^43–47

Why does the vaccine work so well?

Why are vaccine-induced antibody responses so much stronger than those induced by natural HPV infection?

The first reason is that the vaccine, delivered intramuscularly, rapidly enters into blood vessels and the lymphatic system. In contrast, in natural intraepithelial infection, the virus is shed from mucosal surfaces and does not result in viremia.⁴⁸

In addition, the strong immunogenic nature of the virus-like particles induces a robust host antibody response even in the absence of adjuvant because of concentrated neutralizing epitopes and excellent induction of the T-helper cell response.^35,49,50

The neutralizing antibody to L1 prevents HPV infection by blocking HPV from binding to the basement membrane as well as to the epithelial cell receptor during epithelial microabrasion and viral entry. The subsequent micro-wound healing leads to serous exudation and rapid access of serum immunoglobulin G (IgG) to HPV virus particles and encounters with circulatory B memory cells.

Furthermore, emerging evidence suggests that even very low antibody concentrations are sufficient to prevent viral entry into cervical epithelial cells.^{46–48,51–53}

THE HPV VACCINES ARE HIGHLY EFFECTIVE AND SAFE

The efficacy and safety of the quadrivalent and the bivalent HPV vaccines have been evaluated in large randomized clinical trials.^{23,28,29,54,55} Table 1 summarizes the key findings.

The Females United to Unilaterally Reduce Endo/ectocervical Disease (FUTURE I)⁵⁴ and FUTURE II²⁸ trials showed conclusively that the quadrivalent HPV vaccine is 98% to 100% efficacious in preventing HPV 16- and 18-related cervical intraepithelial neoplasia, carcinoma in situ, and invasive cervical cancer in women who had not been infected with HPV before. Similarly, the Papilloma Trial against Cancer in Young Adults (PATRICIA) concluded that the bivalent HPV vaccine is 93% efficacious.²⁹

Giuliano et al⁵⁵ and Palefsky et al²³ conducted randomized clinical trials of the quadrivalent HPV vaccine for preventing genital disease and anal intraepithelial neoplasia in boys and men; the efficacy rates were 90.4%⁵⁵ and 77.5%.²³

A recent Finnish trial in boys age 10 to 18 found 100% seroconversion rates for HPV 16 and HPV 18 antibodies after they received bivalent HPV vaccine.⁵⁶ Similar efficacy has been demonstrated for the quadrivalent HPV vaccine in boys.⁵⁷

Adverse events after vaccination

After the FDA approved the quadrivalent HPV vaccine for girls in 2006, the US Centers for Disease Control and Prevention (CDC) conducted a thorough survey of adverse events after immunization from June 1, 2006 through December 31, 2008.⁵⁸ There were about 54 reports of adverse events per 100,000 distributed vaccine doses, similar to rates for other vaccines. However, the incidence rates of syncope and venous thrombosis were disproportionately higher, according to data from the US Vaccine Adverse Event Reporting System. The rate of syncope was 8.2 per 100,000 vaccine doses, and the rate of venous thrombotic events was 0.2 per 100,000 doses.⁵⁸

There were 32 reports of deaths after HPV vaccination, but these were without clear causation. Hence, this information must be interpreted with caution and should not be used to infer causal associations between HPV vaccines and adverse outcomes. The causes of death included diabetic ketoacidosis, pulmonary embolism, prescription drug abuse, amyotrophic lateral sclerosis, meningoencephalitis, influenza B viral sepsis, arrhythmia, myocarditis, and idiopathic seizure disorder.⁵⁸

Furthermore, it is important to note that vasovagal syncope and venous thromboembolic events are more common in young females in general.⁵⁹ For example, the background rates of venous thromboembolism in females age 14 to 29 using oral contraceptives is 21 to 31 per 100,000 woman-years.⁶⁰

Overall, the quadrivalent HPV vaccine is well tolerated and clinically safe. Postlicensure evaluation found that the quadrivalent and bivalent HPV vaccines had similar safety profiles.⁶¹

Vaccination is contraindicated in people with known hypersensitivity or prior severe allergic reactions to vaccine or yeast or who have bleeding disorders.

HPV VACCINATION DOES MORE THAN PREVENT CERVICAL CANCER IN FEMALES

The quadrivalent HPV vaccine was licensed by the FDA in 2006 for use in females age 9 to 26 to prevent cervical cancer, cervical cancer precursors, vaginal and vulval cancer precursors, and anogenital warts caused by HPV types 6, 11, 16, and 18. The CDC’s Advisory Committee on Immunization Practices (ACIP) issued its recommendation for initiating HPV vaccination for females age 11 to 12 in March 2007. The ACIP stated that the vaccine could be given to girls as early as age 9 and recommended catch-up vaccinations for those age 13 to 26.^62,63

The quadrivalent HPV vaccine was licensed by the FDA in 2009 for use in boys and men for the prevention of genital warts. In December 2010, the quadrivalent HPV vaccine received extended licensure from the FDA for use in males and females for the prevention of anal cancer. In October 2011, the ACIP voted to recommend routine use of the quadrivalent HPV vaccine for boys age 11 to 12; catch-up vaccination should occur for those age 13 to 22, with an option to vaccinate men age 23 to 26.

These recommendations replace the “permissive use” recommendations from the ACIP in October 2009 that said the quadrivalent HPV vaccine may be given to males age 9 to 26.⁶⁴ This shift from a permissive to an active recommendation connotes a positive change reflecting recognition of rising oropharyngeal cancer rates attributable to oncogenic, preventable HPV, rising HPV-related anal cancer incidence, and the burden of the disease in female partners of infected men, with associated rising health care costs.

The bivalent HPV vaccine received FDA licensure in October 2009 for use in females age 10 to 25 to prevent cervical cancer and precursor lesions. The ACIP included the bivalent HPV vaccine in its updated recommendations in May 2010 for use in girls age 11 to 12. Numerous national and international organizations have endorsed HPV vaccination.^65–71

Table 2 outlines the recommendations from these organizations.

HPV VACCINATION RATES ARE STILL LOW

HPV vaccine offers us the hope of eventually eradicating cervical cancer. However, the immunization program still faces many challenges, since HPV vaccination touches on issues related to adolescent sexuality, parental autonomy, and cost. As a result, HPV immunization rates remain relatively low in the United States according to several national surveys. Only 40% to 49% of girls eligible for the vaccine received even one dose, and of those who received even one dose, only 32% to 53.3% came back for all three doses.^72–75 Furthermore, indigent and minority teens were less likely to finish the three-dose HPV vaccine series.

Why are the vaccination rates so low?

Parental barriers. In one survey,⁷³ reasons that parents gave for not having their daughters vaccinated included:

• Lack of knowledge of the vaccine (19.4%)
• Lack of perceived need for the vaccine (18.8%)
• Belief that their daughter was not sexually active (18.3%)
• Clinician not recommending vaccination (13.1%).

In an effort to improve HPV vaccination rates,⁴¹ several states proposed legislation for mandatory HPV vaccination of schoolgirls shortly after licensure of the quadrivalent HPV vaccine.³ Since then, we have seen a wave of public opposition rooted in concerns and misinformation about safety, teenage sexuality, governmental coercion, and cost. Widespread media coverage has also highlighted unsubstantiated claims about side effects attributable to the vaccine that can raise parents’ mistrust of vaccines.⁷⁶ Concerns have also been raised about a threat to parental autonomy in how and when to educate their children about sex.⁷⁷

Moreover, the vaccine has raised ethical concerns in some parents and politicians that mandatory vaccination could undermine abstinence messages in sexual education and may alter sexual activity by condoning risky behavior.⁷⁸ However, a recent study indicated that there is no significant change in sexual behavior related to HPV vaccination in young girls.⁷⁹

In 2012, Mullins et al⁸⁰ also found that an urban population of adolescent girls (76.4% black, 57.5% sexually experienced) did not feel they could forgo safer sexual practices after first HPV vaccination, although the girls did perceive less risk from HPV than from other sexually transmitted infections after HPV vaccination (P < .001).⁸⁰ Inadequate knowledge about HPV-related disease and HPV vaccine correlated with less perceived risk from HPV after vaccination among the girls, and a lack of knowledge about HPV and less communication with their daughters about HPV correlated with less perceived risk from HPV in the mothers of the study population.⁸¹

Health-care-provider barriers. Physician endorsement of vaccines represents a key predictor of vaccine acceptance by patients, families, and other clinicians.^82–84 In 2008, a cross-sectional, Internet-based survey of 1,122 Texas pediatricians, family practice physicians, obstetricians, gynecologists, and internal medicine physicians providing direct patient care found that only 48.5% always recommended HPV vaccination to girls.⁷⁴ Of all respondents, 68.4% were likely to recommend the vaccine to boys, and 41.7% agreed with mandated vaccination. Thus, more than half of the physicians were not following the current recommendations for universal HPV vaccination for 11- to -12-year-olds.

In a survey of 1,013 physicians during the spring and summer of 2009, only 34.6% said they always recommend HPV vaccination to early adolescents, 52.7% to middle adolescents, and 50.2% to late adolescents and young adults.⁸⁵ Pediatricians were more likely than family physicians and obstetrician-gynecologists to always recommend HPV vaccine across all age groups (P < .001). Educational interventions targeting various specialties may help overcome physician-related barriers to immunization.⁸⁵

Financial barriers. HPV vaccine, which must be given in three doses, is more expensive than other vaccines, and this expense is yet another barrier, especially for the uninsured.⁸⁶ Australia launched a government-funded program of HPV vaccination (with the quadrivalent vaccine) in schools in 2007, and it has been very successful. Garland et al⁸⁷ reported that new cases of genital warts have decreased by 73% since the program began, and the rate of high-grade abnormalities on Papanicolaou testing has declined by a small but significant amount.

For HPV vaccination to have an impact on public health, vaccination rates in the general population need to be high. In order to achieve these rates, we need to educate our patients on vaccine safety and efficacy and counsel vaccine recipients about the prevention of sexually transmitted infections and the importance of regular cervical cancer screening after age 21. Clinicians can actively “myth-bust” with patients, who may not realize that the vaccine should be given despite a history of HPV infection or abnormal Pap smear.

FREQUENTLY ASKED QUESTIONS

What if the patient is late for a shot?

The current recommended vaccination schedule for the bivalent and quadrivalent HPV vaccines is a three-dose series administered at 0, 2, and 6 months, given as an intramuscular injection, preferably in the deltoid muscle. The minimal dosing interval is 4 weeks between the first and second doses and 12 weeks between the second and third doses.

The vaccines use different adjuncts with different specific mechanisms for immunogenicity; therefore, it is recommended that the same vaccine be used for the entire three-dose series. However, if circumstances preclude the completion of a series with the same vaccine, the other HPV vaccine may be used.⁶³ Starting the series over is not recommended.

Long-term studies demonstrated clinical efficacy 8.5 years after vaccination.⁴⁷ Amnestic response by virtue of activation of pools of memory B cells has been demonstrated, suggesting the vaccine may afford lifelong immunity.⁸⁸

Is a pregnancy test needed before HPV vaccination?

The ACIP states that pregnancy testing is not required before receiving either of the available HPV vaccines.

A recent retrospective review of phase III efficacy trials and pregnancy registry surveillance data for both vaccines revealed no increase in spontaneous abortions, fetal malformations, or adverse pregnancy outcomes.⁸⁹ Data are limited on bivalent and quadrivalent HPV vaccine given within 30 days of pregnancy and subsequent pregnancy and fetal outcomes. Both vaccines have been assigned a pregnancy rating of category B; however, the ACIP recommends that neither vaccine be given if the recipient is known to be pregnant. If pregnancy occurs, it is recommended that the remainder of the series be deferred until after delivery.⁶²

It is not known whether the vaccine is excreted in breast milk. The manufacturers of both the bivalent and quadrivalent HPV vaccines recommend caution when vaccinating lactating women.^30,31

Can HPV vaccine be given with other vaccines?

In randomized trials, giving the bivalent HPV vaccine with the combined hepatitis A, hepatitis B, meningococcal conjugate and the combined tetanus, diphtheria, and acellular pertussis vaccines did not interfere with the immunogenic response, was safe, and was well tolerated.^90,91 Coadministration of the quadrivalent HPV vaccine has been studied only with hepatitis B vaccine, with similar safety and efficacy noted.

The ACIP recommends giving HPV vaccine at the same visit with other age-appropriate immunizations to increase the likelihood of adherence to recommended vaccination schedules.⁶²

Is HPV vaccination cost-effective?

Kim and Goldie⁸⁶ performed a cost-effectiveness analysis of HPV vaccination of girls at age 12 and catch-up vaccination up to the ages of 18, 21, and 26. For their analysis, they considered prevention of cancers associated with HPV types 16 and 18, of genital warts associated with types 6 and 11, and of recurrent respiratory papillomatosis. They also assumed that immunity would be lifelong, and current screening practices would continue.

They calculated that routine vaccination of 12-year-old girls resulted in an incremental cost-effective ratio of $34,900 per quality-adjusted life-year (QALY) gained. A threshold of less than $50,000 per QALY gained is considered reasonably cost-effective, with an upper limit of $100,000 considered acceptable.⁹²

In the same analysis by Kim and Goldie,⁸⁶ catch-up vaccination of girls through age 18 resulted in a cost of $50,000 to $100,000 per QALY gained, and catch-up vaccination of females through age 26 was significantly less cost-effective at more then $130,000 per QALY gained. The vaccine was also significantly less cost-effective if 5% of the population was neither screened nor vaccinated, if a 10-year booster was required, and if frequent cervical cancer screening intervals were adopted.

This analysis did not include costs related to the evaluation and treatment of abnormal Pap smears and cross-protection against other HPV-related cancers.

The cost-effectiveness of HPV vaccination depends on reaching more girls at younger ages (ideally before sexual debut) and completing the three-dose schedule to optimize duration of immunity.⁹² Appropriate modification of the current recommendations for the intervals of cervical cancer screening for vaccinated individuals will further improve the cost-effectiveness of vaccination. The inclusion of male vaccination generally has more favorable cost per QALY in scenarios in which female coverage rates are less than 50%⁹³ and among men who have sex with men.⁹⁴

TO ERADICATE CERVICAL CANCER

Given the remarkable efficacy and expected long-term immunogenicity of HPV vaccines, we anticipate a decline in HPV-related cervical cancer and other related diseases in the years to come. However, modeling studies predicting the impact of HPV vaccination suggest that although substantial reductions in diseases can be expected, the benefit, assuming high vaccination rates, will not be apparent for at least another decade.⁹⁵ Furthermore, the current HPV vaccines contain only HPV 16 and 18 L1 protein for cancer protection and, therefore, do not provide optimal protection against all oncogenic HPV-related cancers.

The real hope of eradicating cervical cancer and all HPV-related disease relies on a successful global implementation of multivalent HPV vaccination, effective screening strategies, and successful treatment.

The vaccines against human papillomavirus (HPV) are the only ones designed to prevent cancer caused by a virus^1,2—surely a good goal. But because HPV is sexually transmitted, HPV vaccination has met with public controversy.³ To counter the objections and better protect their patients’ health, primary care providers and other clinicians need a clear understanding of the benefits and the low risk of HPV vaccination—and the reasons so many people object to it.³

In this article, we will review:

• The impact of HPV-related diseases
• The basic biologic features of HPV vaccines
• The host immune response to natural HPV infection vs the response to HPV vaccines
• The clinical efficacy and safety of HPV vaccines
• The latest guidelines for HPV vaccination
• The challenges to vaccination implementation
• Frequently asked practical questions about HPV vaccination.

HPV-RELATED DISEASES: FROM BOTHERSOME TO DEADLY

Clinical sequelae of HPV infection include genital warts; cancers of the cervix, vulva, vagina, anus, penis, and oropharynx; and recurrent respiratory papillomatosis.^4–6

Genital warts

HPV types 6 and 11 are responsible for more than 90% of the 1 million new cases of genital warts diagnosed annually in the United States.^7–10

Bothersome and embarrassing, HPV-related genital warts can cause itching, burning, erythema, and pain, as well as epithelial erosions, ulcerations, depigmentation, and urethral and vaginal bleeding and discharge.^11,12 Although they are benign in the oncologic sense, they can cause a good deal of emotional and financial stress. Patients may feel anxiety, embarrassment,¹³ and vulnerability. Adolescents and adults who have or have had genital warts need to inform their current and future partners or else risk infecting them—and facing the consequences.

Direct health care costs of genital warts in the United States have been estimated to be at least $200 million per year.¹⁴

Cervical cancer

Cervical cancer cannot develop unless the cervical epithelium is infected with one of the oncogenic HPV types. Indeed, oncogenic HPV is present in as many as 99.8% of cervical cancer specimens.¹⁵ HPV 16 and 18 are the most oncogenic HPV genotypes and account for 75% of all cases of cervical cancer. Ten other HPV genotypes account for the remaining 25%.¹⁶

In 2012, there were an estimated 12,170 new cases of invasive cervical cancer in the United States and 4,220 related deaths.¹⁷ The cost associated with cervical cancer screening, managing abnormal findings, and treating invasive cervical cancer in the United States is estimated to be $3.3 billion per year.¹⁸

Although the incidence and the mortality rates of cervical cancer have decreased more than 50% in the United States over the past 3 decades thanks to screening,¹⁹ cervical cancer remains the second leading cause of death from cancer in women worldwide. Each year, an estimated 500,000 women contract the disease and 240,000 die of it.²⁰

Anal cancer

A recent study indicated that oncogenic HPV can also cause anal cancer, and the proportion of such cancers associated with HPV 16 or HPV 18 infection is as high as or higher than for cervical cancers, and estimated at 80%.²¹

The incidence of anal cancer is increasing by approximately 2% per year in both men and women in the general population,²² and rates are even higher in men who have sex with men and people infected with the human immunodeficiency virus.²³

Hu and Goldie²⁴ estimated that the lifetime costs of caring for all the people in the United States who in just 1 year (2003) acquired anal cancer attributable to HPV would total $92 million.

Oropharyngeal cancer

HPV types 16, 18, 31, 33, and 35 also cause oropharyngeal cancer. HPV 16 accounts for more than 90% of cases of HPV-related oropharyngeal cancer.²⁵

Chaturvedi et al⁶ tested tissue samples from three national cancer registries and found that the number of oropharyngeal cancers that were HPV-positive increased from 16.3% in 1984–1989 to 71.7% in 2000–2004, while the number of HPV-negative oropharyngeal cancers fell by 50%, paralleling the drop in cigarette smoking in the United States.

Hu and Goldie²⁴ estimated that the total lifetime cost for all new HPV-related oropharyngeal cancers that arose in 2003 would come to $38.1 million.²⁴

Vulvar and vaginal cancers

HPV 16 and 18 are also responsible for approximately 50% of vulvar cancers and 50% to 75% of vaginal cancers.^4,5

Recurrent respiratory papillomatosis

HPV 6 and 11 cause almost all cases of juvenile- and adult-onset recurrent respiratory papillomatosis.²⁶ The annual cost for surgical procedures for this condition in the United States has been estimated at $151 million.²⁷

HPV VACCINES ARE NONINFECTIOUS AND NONCARCINOGENIC

Currently, two HPV vaccines are available: a quadrivalent vaccine against types 6, 11, 16, and 18 (Gardasil; Merck) and a bivalent vaccine against types 16 and 18 (Cervarix; Glaxo-SmithKline). The quadrivalent vaccine was approved by the US Food and Drug Administration (FDA) in 2006, and the bivalent vaccine was approved in 2009.^28,29

Both vaccines contain virus-like particles, ie, viral capsids that contain no DNA. HPV has a circular DNA genome of 8,000 nucleotides divided into two regions: the early region, for viral replication, and the late region, for viral capsid production. The host produces neutralizing antibodies in response to the L1 capsid protein, which is different in different HPV types.

In manufacturing the vaccines, the viral L1 gene is incorporated into a yeast genome or an insect virus genome using recombinant DNA technology (Figure 1). Grown in culture, the yeast or the insect cells produce the HPV L1 major capsid protein, which has the intrinsic capacity to self-assemble into virus-like particles.^30–33 These particles are subsequently purified for use in the vaccines.³⁴

Recombinant virus-like particles are morphologically indistinguishable from authentic HPV virions and contain the same typespecific antigens present in authentic virions. Therefore, they are highly effective in inducing a host humoral immune response. And because they do not contain HPV DNA, the recombinant HPV vaccines are noninfectious and noncarcinogenic.³⁵

VACCINATION INDUCES A STRONGER IMMUNE RESPONSE THAN INFECTION

HPV infections trigger both a humoral and a cellular response in the host immune system.

The humoral immune response to HPV infection involves producing neutralizing antibody against the specific HPV type, specifically the specific L1 major capsid protein. This process is typically somewhat slow and weak, and only about 60% of women with a new HPV infection develop antibodies to it.^36,37

HPV has several ways to evade the host immune system. It does not infect or replicate within the antigen-presenting cells in the epithelium. In addition, HPV-infected keratinocytes are less susceptible to cytotoxic lymphocytic-mediated lysis. Moreover, HPV infection cause very little tissue destruction. And finally, natural cervical HPV infection does not result in viremia. As a result, antigen-presenting cells have no chance to engulf the virions and present virion-derived antigen to the host immune system. The immune system outside the epithelium has limited opportunity to detect the virus because HPV infection does not have a blood-borne phase.^38,39

The cell-mediated immune response to early HPV oncoproteins may help eliminate established HPV infection.⁴⁰ In contrast to antibodies, the T-cell response to HPV has not been shown to be specific to HPV type.⁴¹ Clinically, cervical HPV infection is common, but most lesions go into remission or resolve as a result of the cell-mediated immune response.^40,41

In contrast to the weak, somewhat ineffective immune response to natural HPV infection, the antibody response to HPV vaccines is rather robust. In randomized controlled trials, almost all vaccinated people have seroconverted. The peak antibody concentrations are 50 to 10,000 times greater than in natural infection. Furthermore, the neutralizing antibodies induced by HPV vaccines persist for as long as 7 to 9 years after immunization.⁴² However, the protection provided by HPV vaccines against HPV-related cervical intraepithelial neoplasia does not necessarily correlate with the antibody concentration.^43–47

Why does the vaccine work so well?

Why are vaccine-induced antibody responses so much stronger than those induced by natural HPV infection?

The first reason is that the vaccine, delivered intramuscularly, rapidly enters into blood vessels and the lymphatic system. In contrast, in natural intraepithelial infection, the virus is shed from mucosal surfaces and does not result in viremia.⁴⁸

In addition, the strong immunogenic nature of the virus-like particles induces a robust host antibody response even in the absence of adjuvant because of concentrated neutralizing epitopes and excellent induction of the T-helper cell response.^35,49,50

The neutralizing antibody to L1 prevents HPV infection by blocking HPV from binding to the basement membrane as well as to the epithelial cell receptor during epithelial microabrasion and viral entry. The subsequent micro-wound healing leads to serous exudation and rapid access of serum immunoglobulin G (IgG) to HPV virus particles and encounters with circulatory B memory cells.

Furthermore, emerging evidence suggests that even very low antibody concentrations are sufficient to prevent viral entry into cervical epithelial cells.^{46–48,51–53}

THE HPV VACCINES ARE HIGHLY EFFECTIVE AND SAFE

The efficacy and safety of the quadrivalent and the bivalent HPV vaccines have been evaluated in large randomized clinical trials.^{23,28,29,54,55} Table 1 summarizes the key findings.

The Females United to Unilaterally Reduce Endo/ectocervical Disease (FUTURE I)⁵⁴ and FUTURE II²⁸ trials showed conclusively that the quadrivalent HPV vaccine is 98% to 100% efficacious in preventing HPV 16- and 18-related cervical intraepithelial neoplasia, carcinoma in situ, and invasive cervical cancer in women who had not been infected with HPV before. Similarly, the Papilloma Trial against Cancer in Young Adults (PATRICIA) concluded that the bivalent HPV vaccine is 93% efficacious.²⁹

Giuliano et al⁵⁵ and Palefsky et al²³ conducted randomized clinical trials of the quadrivalent HPV vaccine for preventing genital disease and anal intraepithelial neoplasia in boys and men; the efficacy rates were 90.4%⁵⁵ and 77.5%.²³

A recent Finnish trial in boys age 10 to 18 found 100% seroconversion rates for HPV 16 and HPV 18 antibodies after they received bivalent HPV vaccine.⁵⁶ Similar efficacy has been demonstrated for the quadrivalent HPV vaccine in boys.⁵⁷

Adverse events after vaccination

After the FDA approved the quadrivalent HPV vaccine for girls in 2006, the US Centers for Disease Control and Prevention (CDC) conducted a thorough survey of adverse events after immunization from June 1, 2006 through December 31, 2008.⁵⁸ There were about 54 reports of adverse events per 100,000 distributed vaccine doses, similar to rates for other vaccines. However, the incidence rates of syncope and venous thrombosis were disproportionately higher, according to data from the US Vaccine Adverse Event Reporting System. The rate of syncope was 8.2 per 100,000 vaccine doses, and the rate of venous thrombotic events was 0.2 per 100,000 doses.⁵⁸

There were 32 reports of deaths after HPV vaccination, but these were without clear causation. Hence, this information must be interpreted with caution and should not be used to infer causal associations between HPV vaccines and adverse outcomes. The causes of death included diabetic ketoacidosis, pulmonary embolism, prescription drug abuse, amyotrophic lateral sclerosis, meningoencephalitis, influenza B viral sepsis, arrhythmia, myocarditis, and idiopathic seizure disorder.⁵⁸

Furthermore, it is important to note that vasovagal syncope and venous thromboembolic events are more common in young females in general.⁵⁹ For example, the background rates of venous thromboembolism in females age 14 to 29 using oral contraceptives is 21 to 31 per 100,000 woman-years.⁶⁰

Overall, the quadrivalent HPV vaccine is well tolerated and clinically safe. Postlicensure evaluation found that the quadrivalent and bivalent HPV vaccines had similar safety profiles.⁶¹

Vaccination is contraindicated in people with known hypersensitivity or prior severe allergic reactions to vaccine or yeast or who have bleeding disorders.

HPV VACCINATION DOES MORE THAN PREVENT CERVICAL CANCER IN FEMALES

The quadrivalent HPV vaccine was licensed by the FDA in 2006 for use in females age 9 to 26 to prevent cervical cancer, cervical cancer precursors, vaginal and vulval cancer precursors, and anogenital warts caused by HPV types 6, 11, 16, and 18. The CDC’s Advisory Committee on Immunization Practices (ACIP) issued its recommendation for initiating HPV vaccination for females age 11 to 12 in March 2007. The ACIP stated that the vaccine could be given to girls as early as age 9 and recommended catch-up vaccinations for those age 13 to 26.^62,63

The quadrivalent HPV vaccine was licensed by the FDA in 2009 for use in boys and men for the prevention of genital warts. In December 2010, the quadrivalent HPV vaccine received extended licensure from the FDA for use in males and females for the prevention of anal cancer. In October 2011, the ACIP voted to recommend routine use of the quadrivalent HPV vaccine for boys age 11 to 12; catch-up vaccination should occur for those age 13 to 22, with an option to vaccinate men age 23 to 26.

These recommendations replace the “permissive use” recommendations from the ACIP in October 2009 that said the quadrivalent HPV vaccine may be given to males age 9 to 26.⁶⁴ This shift from a permissive to an active recommendation connotes a positive change reflecting recognition of rising oropharyngeal cancer rates attributable to oncogenic, preventable HPV, rising HPV-related anal cancer incidence, and the burden of the disease in female partners of infected men, with associated rising health care costs.

The bivalent HPV vaccine received FDA licensure in October 2009 for use in females age 10 to 25 to prevent cervical cancer and precursor lesions. The ACIP included the bivalent HPV vaccine in its updated recommendations in May 2010 for use in girls age 11 to 12. Numerous national and international organizations have endorsed HPV vaccination.^65–71

Table 2 outlines the recommendations from these organizations.

HPV VACCINATION RATES ARE STILL LOW

HPV vaccine offers us the hope of eventually eradicating cervical cancer. However, the immunization program still faces many challenges, since HPV vaccination touches on issues related to adolescent sexuality, parental autonomy, and cost. As a result, HPV immunization rates remain relatively low in the United States according to several national surveys. Only 40% to 49% of girls eligible for the vaccine received even one dose, and of those who received even one dose, only 32% to 53.3% came back for all three doses.^72–75 Furthermore, indigent and minority teens were less likely to finish the three-dose HPV vaccine series.

Why are the vaccination rates so low?

Parental barriers. In one survey,⁷³ reasons that parents gave for not having their daughters vaccinated included:

• Lack of knowledge of the vaccine (19.4%)
• Lack of perceived need for the vaccine (18.8%)
• Belief that their daughter was not sexually active (18.3%)
• Clinician not recommending vaccination (13.1%).

In an effort to improve HPV vaccination rates,⁴¹ several states proposed legislation for mandatory HPV vaccination of schoolgirls shortly after licensure of the quadrivalent HPV vaccine.³ Since then, we have seen a wave of public opposition rooted in concerns and misinformation about safety, teenage sexuality, governmental coercion, and cost. Widespread media coverage has also highlighted unsubstantiated claims about side effects attributable to the vaccine that can raise parents’ mistrust of vaccines.⁷⁶ Concerns have also been raised about a threat to parental autonomy in how and when to educate their children about sex.⁷⁷

Moreover, the vaccine has raised ethical concerns in some parents and politicians that mandatory vaccination could undermine abstinence messages in sexual education and may alter sexual activity by condoning risky behavior.⁷⁸ However, a recent study indicated that there is no significant change in sexual behavior related to HPV vaccination in young girls.⁷⁹

In 2012, Mullins et al⁸⁰ also found that an urban population of adolescent girls (76.4% black, 57.5% sexually experienced) did not feel they could forgo safer sexual practices after first HPV vaccination, although the girls did perceive less risk from HPV than from other sexually transmitted infections after HPV vaccination (P < .001).⁸⁰ Inadequate knowledge about HPV-related disease and HPV vaccine correlated with less perceived risk from HPV after vaccination among the girls, and a lack of knowledge about HPV and less communication with their daughters about HPV correlated with less perceived risk from HPV in the mothers of the study population.⁸¹

Health-care-provider barriers. Physician endorsement of vaccines represents a key predictor of vaccine acceptance by patients, families, and other clinicians.^82–84 In 2008, a cross-sectional, Internet-based survey of 1,122 Texas pediatricians, family practice physicians, obstetricians, gynecologists, and internal medicine physicians providing direct patient care found that only 48.5% always recommended HPV vaccination to girls.⁷⁴ Of all respondents, 68.4% were likely to recommend the vaccine to boys, and 41.7% agreed with mandated vaccination. Thus, more than half of the physicians were not following the current recommendations for universal HPV vaccination for 11- to -12-year-olds.

In a survey of 1,013 physicians during the spring and summer of 2009, only 34.6% said they always recommend HPV vaccination to early adolescents, 52.7% to middle adolescents, and 50.2% to late adolescents and young adults.⁸⁵ Pediatricians were more likely than family physicians and obstetrician-gynecologists to always recommend HPV vaccine across all age groups (P < .001). Educational interventions targeting various specialties may help overcome physician-related barriers to immunization.⁸⁵

Financial barriers. HPV vaccine, which must be given in three doses, is more expensive than other vaccines, and this expense is yet another barrier, especially for the uninsured.⁸⁶ Australia launched a government-funded program of HPV vaccination (with the quadrivalent vaccine) in schools in 2007, and it has been very successful. Garland et al⁸⁷ reported that new cases of genital warts have decreased by 73% since the program began, and the rate of high-grade abnormalities on Papanicolaou testing has declined by a small but significant amount.

For HPV vaccination to have an impact on public health, vaccination rates in the general population need to be high. In order to achieve these rates, we need to educate our patients on vaccine safety and efficacy and counsel vaccine recipients about the prevention of sexually transmitted infections and the importance of regular cervical cancer screening after age 21. Clinicians can actively “myth-bust” with patients, who may not realize that the vaccine should be given despite a history of HPV infection or abnormal Pap smear.

FREQUENTLY ASKED QUESTIONS

What if the patient is late for a shot?

The current recommended vaccination schedule for the bivalent and quadrivalent HPV vaccines is a three-dose series administered at 0, 2, and 6 months, given as an intramuscular injection, preferably in the deltoid muscle. The minimal dosing interval is 4 weeks between the first and second doses and 12 weeks between the second and third doses.

The vaccines use different adjuncts with different specific mechanisms for immunogenicity; therefore, it is recommended that the same vaccine be used for the entire three-dose series. However, if circumstances preclude the completion of a series with the same vaccine, the other HPV vaccine may be used.⁶³ Starting the series over is not recommended.

Long-term studies demonstrated clinical efficacy 8.5 years after vaccination.⁴⁷ Amnestic response by virtue of activation of pools of memory B cells has been demonstrated, suggesting the vaccine may afford lifelong immunity.⁸⁸

Is a pregnancy test needed before HPV vaccination?

The ACIP states that pregnancy testing is not required before receiving either of the available HPV vaccines.

A recent retrospective review of phase III efficacy trials and pregnancy registry surveillance data for both vaccines revealed no increase in spontaneous abortions, fetal malformations, or adverse pregnancy outcomes.⁸⁹ Data are limited on bivalent and quadrivalent HPV vaccine given within 30 days of pregnancy and subsequent pregnancy and fetal outcomes. Both vaccines have been assigned a pregnancy rating of category B; however, the ACIP recommends that neither vaccine be given if the recipient is known to be pregnant. If pregnancy occurs, it is recommended that the remainder of the series be deferred until after delivery.⁶²

It is not known whether the vaccine is excreted in breast milk. The manufacturers of both the bivalent and quadrivalent HPV vaccines recommend caution when vaccinating lactating women.^30,31

Can HPV vaccine be given with other vaccines?

In randomized trials, giving the bivalent HPV vaccine with the combined hepatitis A, hepatitis B, meningococcal conjugate and the combined tetanus, diphtheria, and acellular pertussis vaccines did not interfere with the immunogenic response, was safe, and was well tolerated.^90,91 Coadministration of the quadrivalent HPV vaccine has been studied only with hepatitis B vaccine, with similar safety and efficacy noted.

The ACIP recommends giving HPV vaccine at the same visit with other age-appropriate immunizations to increase the likelihood of adherence to recommended vaccination schedules.⁶²

Is HPV vaccination cost-effective?

Kim and Goldie⁸⁶ performed a cost-effectiveness analysis of HPV vaccination of girls at age 12 and catch-up vaccination up to the ages of 18, 21, and 26. For their analysis, they considered prevention of cancers associated with HPV types 16 and 18, of genital warts associated with types 6 and 11, and of recurrent respiratory papillomatosis. They also assumed that immunity would be lifelong, and current screening practices would continue.

They calculated that routine vaccination of 12-year-old girls resulted in an incremental cost-effective ratio of $34,900 per quality-adjusted life-year (QALY) gained. A threshold of less than $50,000 per QALY gained is considered reasonably cost-effective, with an upper limit of $100,000 considered acceptable.⁹²

In the same analysis by Kim and Goldie,⁸⁶ catch-up vaccination of girls through age 18 resulted in a cost of $50,000 to $100,000 per QALY gained, and catch-up vaccination of females through age 26 was significantly less cost-effective at more then $130,000 per QALY gained. The vaccine was also significantly less cost-effective if 5% of the population was neither screened nor vaccinated, if a 10-year booster was required, and if frequent cervical cancer screening intervals were adopted.

This analysis did not include costs related to the evaluation and treatment of abnormal Pap smears and cross-protection against other HPV-related cancers.

The cost-effectiveness of HPV vaccination depends on reaching more girls at younger ages (ideally before sexual debut) and completing the three-dose schedule to optimize duration of immunity.⁹² Appropriate modification of the current recommendations for the intervals of cervical cancer screening for vaccinated individuals will further improve the cost-effectiveness of vaccination. The inclusion of male vaccination generally has more favorable cost per QALY in scenarios in which female coverage rates are less than 50%⁹³ and among men who have sex with men.⁹⁴

TO ERADICATE CERVICAL CANCER

Given the remarkable efficacy and expected long-term immunogenicity of HPV vaccines, we anticipate a decline in HPV-related cervical cancer and other related diseases in the years to come. However, modeling studies predicting the impact of HPV vaccination suggest that although substantial reductions in diseases can be expected, the benefit, assuming high vaccination rates, will not be apparent for at least another decade.⁹⁵ Furthermore, the current HPV vaccines contain only HPV 16 and 18 L1 protein for cancer protection and, therefore, do not provide optimal protection against all oncogenic HPV-related cancers.

The real hope of eradicating cervical cancer and all HPV-related disease relies on a successful global implementation of multivalent HPV vaccination, effective screening strategies, and successful treatment.

In Reply: We thank Dr. Keller for his excellent comment. The rationale for discontinuing screening in a woman over 70 who has multiple sexual partners without a history of an abnormal Pap test is that she is at lower risk of new-onset cervical intraepithelial neoplasia (CIN) than a younger woman because of her decreased rate of metaplasia and less accessible transformation zone. In addition, postmenopausal mucosal atrophy may predispose to false-positive cytology. False-positive results are likely to be followed by additional invasive procedures, anxiety, and cost to the patient. However, she is still at risk for acquiring human papillomavirus (HPV) and CIN. Given that cervical cancer develops slowly and risk factors decrease with age, it is reasonable to stop screening at this point. Also, the recommendation of the 3-year screening interval in women over 30 with multiple sexual partners who had negative Pap and HPV tests is based on the fact that they can acquire HPV the day after screening and subsequently develop CIN, but we can detect HPV and CIN in the next round of screening (3 years later) and so will not miss the opportunity to treat cervical dysplasia.

However, practice guidelines are never meant to replace a physician’s sound clinical decision made on an individual basis.

In Reply: We thank Dr. Keller for his excellent comment. The rationale for discontinuing screening in a woman over 70 who has multiple sexual partners without a history of an abnormal Pap test is that she is at lower risk of new-onset cervical intraepithelial neoplasia (CIN) than a younger woman because of her decreased rate of metaplasia and less accessible transformation zone. In addition, postmenopausal mucosal atrophy may predispose to false-positive cytology. False-positive results are likely to be followed by additional invasive procedures, anxiety, and cost to the patient. However, she is still at risk for acquiring human papillomavirus (HPV) and CIN. Given that cervical cancer develops slowly and risk factors decrease with age, it is reasonable to stop screening at this point. Also, the recommendation of the 3-year screening interval in women over 30 with multiple sexual partners who had negative Pap and HPV tests is based on the fact that they can acquire HPV the day after screening and subsequently develop CIN, but we can detect HPV and CIN in the next round of screening (3 years later) and so will not miss the opportunity to treat cervical dysplasia.

However, practice guidelines are never meant to replace a physician’s sound clinical decision made on an individual basis.

In Reply: We thank Dr. Keller for his excellent comment. The rationale for discontinuing screening in a woman over 70 who has multiple sexual partners without a history of an abnormal Pap test is that she is at lower risk of new-onset cervical intraepithelial neoplasia (CIN) than a younger woman because of her decreased rate of metaplasia and less accessible transformation zone. In addition, postmenopausal mucosal atrophy may predispose to false-positive cytology. False-positive results are likely to be followed by additional invasive procedures, anxiety, and cost to the patient. However, she is still at risk for acquiring human papillomavirus (HPV) and CIN. Given that cervical cancer develops slowly and risk factors decrease with age, it is reasonable to stop screening at this point. Also, the recommendation of the 3-year screening interval in women over 30 with multiple sexual partners who had negative Pap and HPV tests is based on the fact that they can acquire HPV the day after screening and subsequently develop CIN, but we can detect HPV and CIN in the next round of screening (3 years later) and so will not miss the opportunity to treat cervical dysplasia.

However, practice guidelines are never meant to replace a physician’s sound clinical decision made on an individual basis.

Cervical cancer screening and prevention have evolved rapidly in the last decade, especially in the 5 years since the introduction of the first cancer prevention vaccine, human papillomavirus (HPV) recombinant vaccine.¹

Providers need to understand the rationale for the recommendations so that they can explain them to patients. In particular, patients may wonder why we now begin screening for cervical cancer later than we used to, and why some women do not need to be screened as often. Both of these changes result from our enhanced understanding of the role of HPV in cervical cancer genesis.

In this article we will briefly review:

• The current understanding of the natural history of cervical cancer
• Advantages and disadvantages of cervical cytology, ie, the Papanicolaou (Pap) test
• The role of HPV testing in cervical cancer screening
• The latest screening guidelines (the new standard of care)
• A possible future screening strategy
• The impact of HPV vaccination on screening.

500,000 NEW CASES EVERY YEAR

The incidence of cervical cancer and its mortality rate have decreased more than 50% in the United States over the past 3 decades, largely as a result of screening with the Pap test.² In 2010, there were an estimated 12,200 new cases of invasive cervical cancer in the United States and 4,210 deaths from it,³ which are lower than the historical rates.

However, because most developing countries lack effective screening programs, cervical cancer remains the second-leading cause of death from cancer in women worldwide. According to a recent estimate, there are almost 500,000 new cases and 240,000 deaths from this disease worldwide every year.⁴ If effective global screening programs could be set up, they would markedly reduce the incidence of cervical cancer and deaths from it.⁵

HPV IS NECESSARY BUT NOT SUFFICIENT FOR CERVICAL CANCER TO DEVELOP

For cervical cancer to develop, the essential first step is infection of the cervical epithelium with one of the oncogenic (high-risk) types of HPV (see below).^6–10 Walboomers et al⁹ tested cervical tissue samples taken from 932 women with cervical cancer and detected HPV DNA in 930 (99.8%) of them.

Fortunately, most HPV-infected women do not develop cervical cancer, as most young women clear the infection in an average of 8 to 24 months.^11,12 However, if the infection persists, and if it is one of the high-risk types of HPV, precursor lesions can develop that can progress to cervical cancer.¹³ The evidence conclusively supports the association between oncogenic HPV infection and the subsequent development of virtually all cases of cervical cancer.^6–10

Known risk factors for HPV persistence and the subsequent development of high-grade lesions are cigarette smoking and a compromised immune system.^14,15

Terminology: Results of Pap smears

• Normal
• Atypical squamous cells of undetermined significance (ASC-US)
• Low-grade squamous intraepithelial lesions (LSIL)
• High-grade squamous intraepithelial lesions (HSIL)
• Cancer.

Terminology: Results of cervical biopsy

• Normal
• Cervical intraepithelial neoplasia grade 1 (CIN1)
• CIN2 (previously called moderate dysplasia)
• CIN3 (previously called severe dysplasia)
• Carcinoma in situ
• Invasive cervical cancer.

Lesions that are CIN2 or higher are considered high-grade.¹³

The 18 high-risk HPV types

More than 40 types of HPV infect the genital tract¹⁶; 18 of these (types 16, 18, 26, 31, 33, 35, 39, 45, 51, 52, 53, 56, 58, 59, 66, 68, 73, and 82) are classified as high-risk because of their causative association with cervical cancer (ie, their oncogenic potential).¹⁷

How HPV causes cervical cancer

In laboratory cultures, normal human cells die out after a few generations. However, if human epithelial cells are infected by one of the high-risk types of HPV, they can go on dividing indefinitely.^18,19

Two HPV proteins, E6 and E7, induce this cell “immortalization.”^20,21 E6 from high-risk HPV binds to the human tumor-suppressor protein p53 and rapidly degrades it in a proteolytic process. The p53 protein normally suppresses cell proliferation by arresting growth in the G1 phase of the cell cycle. Therefore, with less p53, the cell cannot suppress uncontrolled cell growth.^22–24

Similarly, E7 from high-risk HPV forms a complex with another human tumor suppressor, the retinoblastoma protein (pRB), and disrupts its binding to a transcriptional factor, E2F-1. The freed E2F-1 then stimulates DNA synthesis and uncontrolled cell growth.²⁵

Furthermore, HPV-16 E6 and E7 proteins can collectively cause cellular genetic instability.²⁶

The carcinogenic mechanism of high-risk HPV is complex. The host immune system and natural tumor suppression play important roles. However, the natural history of cervical intraepithelial neoplasia is not well understood. For example, it remains unclear if low-grade lesions such as CIN1 are necessary precursors to high-grade lesions and invasive cancer.^6,7,10

THE PAP TEST: SPECIFIC BUT NOT VERY SENSITIVE, AND PRONE TO ERROR

The principal advantage of cervical cytologic testing (ie, the Pap test) in detecting cervical dysplasia is its overall high specificity. Many studies have found that the specificity of conventional Pap testing can reach approximately 98%.²⁷

However, the conventional Pap test has drawbacks. Contaminants such as blood, discharge, and lubricant can make it difficult to interpret, and artifact can occur with air-drying of the Pap smear as it is transferred to the cell slide (“air-drying artifact”).

Liquid-based cytologic study has replaced the older method

To overcome these disadvantages, a liquid-based method of cervical cytologic study, ThinPrep (Hologic, Bedford, MA), was introduced in the mid-1990s. In this method, cell samples are first transferred to a liquid solution for mechanical separation from contaminants, and a representative sample of cells is then placed on a slide for review.

The liquid-based method filters out most contaminating blood, inflammatory cells, and debris. It also eliminates the air-drying artifact in the conventional Pap collection technique and improves specimen adequacy. Cytotechnologists find liquid-based specimens easier to read because the cells are more evenly distributed on a clearer background. Another advantage is that we can routinely test for HPV in the available residual specimen if the cytologic interpretation is abnormal.

The main disadvantages of the liquid-based method are that its specificity is lower than that of conventional Pap smears (around 78%) and that it costs more.²⁸ Nevertheless, the liquid-based technique has become the main method of cervical cytology, used by nearly 90% of gynecologists in the United States since 2003.¹

Cytology is still prone to false-negative results

Despite the success of both conventional Pap testing and liquid-based Pap testing, cervical cytology is inherently prone to sample-quality variation, subjective interpretation error, and false-negative results. False-negative results can be due to failure to transfer dysplastic cells to the slide or failure of the cytologist to recognize abnormal cells. In 30% of new cases of cervical cancer, the patient had recently had a Pap test that was interpreted as negative.^1,29

Errors in interpretation are exacerbated by inconsistency among cytopathologists. In one study,^6,30 when a group of quality-control pathologists reviewed nearly 5,000 cytology specimens, they came to the same conclusion that the original reviewers did more than 50% of the time only for negative and LSIL readings. Of the specimens initially reported as ASC-US, almost 40% were reclassified as negative on further review. Of those originally interpreted as HSIL, more than 50% were reclassified as LSIL, as ASC-US, or as negative.

Furthermore, many studies found that the sensitivity of conventional Pap testing was only around 50%.²⁷ The new liquid-based Pap test uses computer imaging, which has improved the rate of detection of cervical dysplasia but may still miss 15% to 35% of cases of HSIL (severe dysplasia) or cancer.³¹ Failure to detect cervical dysplasia or cancer on Pap smear has led to a number of lawsuits.³²

Clearly, with its relatively low sensitivity, cervical cytology is no longer good enough to use as a sole screening test in all situations. However, its high specificity is an advantage when it is combined with HPV testing in screening.

HPV TESTING AND PAP TESTING COMPLEMENT EACH OTHER

From 17% to 36% of HPV-infected women develop a cytologic abnormality within 5 years, compared with 4% to 15% of women who are HPV-negative.^33,34

The usefulness of testing for HPV in women who have had an abnormal Pap test has been well demonstrated in multiple studies.^35–38

The landmark Atypical Squamous Cells of Undetermined Significance/Low-Grade Squamous Intraepithelial Lesions Triage Study (ALTS)³⁹ found that 82.9% of women with LSIL were HPV-positive. The investigators concluded that HPV testing has little utility in women with LSIL, as the test would likely be positive and thus would not change the decision to perform colposcopy.

However, in women with ASC-US, the sensitivity of HPV testing for predicting CIN3 or cancer was 96.3% and the negative predictive value was 99.5%. In contrast, the sensitivity of a single repeat Pap test was only 44.1%. This large randomized trial conclusively validates the important role of HPV testing in triaging women with ASC-US.

More recently, a meta-analysis of 20 studies of HPV testing in women with ASC-US found that it had a sensitivity of 92.5% and a specificity of 62.5% for detecting CIN2 or worse lesions, and a sensitivity of 95.6% and a specificity of 59.2% for detecting CIN3 or worse lesions.⁴⁰

Furthermore, HPV testing in primary cervical cancer screening is strongly supported by large cross-sectional studies^41–45 and randomized clinical trials.^46,47 These studies have conclusively shown that HPV testing is significantly more sensitive than Pap testing for detecting cervical intraepithelial neoplasia, and that, when combined with Pap testing, it can achieve nearly 100% clinical sensitivity and nearly 93% specificity in women age 30 or older. Women who have negative results on both the HPV test and the Pap test can be reassured that their risk of undetected CIN2, CIN3, or cervical cancer is extremely low, since HPV testing has a negative predictive value close to 100%.⁴⁶

In large multinational European studies involving more than 24,000 women, the risk of CIN3 or cancer after 6 years of follow-up was only 0.28% in women who had negative results on both HPV and Pap testing at baseline. This rate was basically the same as in women who tested negative for HPV alone (0.27%). However, it was significantly lower than that of all women who had negative Pap test results (0.97%). The combination of HPV testing and Pap testing at 6-year intervals offered better protection than Pap testing alone at 3-year intervals.⁴⁸

NEW STANDARD OF CARE: THE LATEST SCREENING GUIDELINES

Until the mid-1990s, the strategy for cervical cancer screening had remained largely unchanged for many years. Since then, several advances have prompted changes in the standard of care.

1996—The US Food and Drug Administration (FDA) approved liquid-based Thin-Prep for cervical cancer screening, which improved specimen adequacy and reduced ambiguous interpretations compared with the original slide-based method of collection.⁴⁹

2001—The Bethesda terminology for reporting cervical cytology results was updated. First proposed in 1988 to replace the original Papanicolaou system and revised in 1991, this standardized terminology enabled better clinical decision-making.⁵⁰

2001—The FDA approved HPV testing for women with ASC-US. This provided a better triage strategy for deciding which women need colposcopy to exclude true intraepithelial lesions. Following the FDA approval, the clinical effectiveness of HPV testing in women with ASC-US was validated by a large randomized clinical trial—the ALTS.⁵¹

2003—The FDA approved HPV testing in conjunction with Pap testing for women age 30 or older in routine primary screening.⁵²

Guidelines available

Based on these new developments in technology and reporting terminology, and the incorporation of HPV testing, several organizations issued guidelines.

The American Society for Colposcopy and Cervical Pathology published a consensus guideline on management of abnormal cervical cytology in 2001 and revised it in 2006.⁵³

The American Cancer Society issued its guideline for cervical cancer screening in 2002.⁵⁴

The US Preventive Services Task Force published its screening guidelines in 2003.⁵⁵

The American College of Obstetricians and Gynecologists (ACOG) also made new recommendations in 2003 and updated them in December 2009.¹

Start screening at age 21

Cervical cancer screening should begin at age 21 regardless of the age of onset of vaginal intercourse, according to the 2009 ACOG guidelines.¹ This represents a change from previous recommendations from ACOG, the American Cancer Society, and the US Preventive Services Task Force, which were to start screening within 3 years of the onset of vaginal intercourse.

Rationale. This latest recommendation is based on the high rates of clearance of HPV infection and of spontaneous dysplasia regression and the low incidence of cervical cancer in younger women.^57,58 HPV infections are common in young women who have had vaginal intercourse. However, most such HPV infections are cleared by the immune system within 1 to 2 years without causing cervical dysplasia.^11,12 Invasive cervical cancer in women younger than 21 years is very rare. The annual incidence is only one to two cases per 1 million women ages 15 to 19.^2,55

Another reason for not screening before age 21 is that a positive test result may lead to unnecessary anxiety and potentially harmful evaluations and procedures.

Screening intervals extended

The 2009 ACOG guidelines lengthen the cervical cancer screening interval to every 2 years in women under age 30.¹ (The 2003 ACOG guidelines said to screen every year.)

For women age 30 and older, the 2009 ACOG guidelines recommend extending the interval to every 3 years when combined Pap and HPV testing are negative (changed from every 2 to 3 years).¹

Rationale. Studies have shown little advantage in screening every year in women under the age of 30, with no higher risk of cervical cancer in women screened at a 2- to 3-year interval.^59–62 The absolute risk of cervical cancer in a well-screened population is very low.⁶³ Moreover, the absolute number of cervical cancer cases in women age 30 to 64 years screened at 3-year intervals is only four per 100,000 women.⁶⁴

HPV-plus-Pap testing for women over 30

Based on convincing evidence of the high sensitivity and the high negative predictive value of HPV testing, since 2003 ACOG had recommended HPV-plus-Pap testing in women over age 30. Its 2009 guidelines upgraded this recommendation to level A, ie, the highest grade, based on good and consistent scientific evidence.¹ (Previously the recommendation was level B.)

The American Cancer Society also recommends combined HPV and Pap testing as the optimal screening approach in women age 30 or older, with the subsequent screening interval 3 years if both tests are negative. It also endorses Pap testing alone every 2 to 3 years as an alternative screening strategy in this age group.

The US Preventive Services Task Force recommends Pap testing every 3 years in women age 30 or older, and it does not recommend for or against HPV testing. However, neither the US Preventive Services Task Force nor the American Cancer Society has updated its guidelines in 8 years.

Rationale. Women who undergo HPV-plus-Pap testing and who test negative on both are at very low risk of developing CIN2 or CIN3 during the next 4 to 6 years. The risk is much lower than that for women who have a sole negative Pap test result.^39,40 Because of this extremely high negative predictive value, women age 30 and older who had negative results on both Pap and HPV testing should be screened no more often than every 3 years.

We believe that the HPV-plus-Pap testing strategy recommended by the 2009 ACOG guidelines for women age 30 and older is the most effective screening approach. This strategy takes advantage of the high sensitivity and high negative predictive value of HPV testing, as well as the high specificity of Pap testing. It achieves almost 100% clinical sensitivity in detecting cervical dysplasia.⁴⁶

The 2009 ACOG guidelines for the first time call for stopping cervical cancer screening in women 65 to 70 years of age who have had three negative Pap tests in a row and no abnormal tests in the previous 10 years.¹ The American Cancer Society recommends stopping screening at age 70,⁶⁵ while the US Preventive Services Task Force recommends stopping at age 65.⁵⁵

Rationale. Cervical cancer develops slowly, and risk factors tend to decline with age, Also, postmenopausal mucosal atrophy may predispose to false-positive Pap results, which can lead to additional procedures and unnecessary patient anxiety.⁶⁶

However, it is probably reasonable to continue screening in women age 70 and older who are sexually active with multiple partners and who have a history of abnormal Pap test results.¹

Women who have had a hysterectomy

According to the latest American Cancer Society, ACOG, and US Preventive Services Task Force guidelines, cervical cancer screening should be discontinued after total hysterectomy for benign indications in women who have no history of high-grade cervical intraepithelial neoplasia, ie, CIN2 or worse.¹

Rationale. If the patient has no cervix, continued vaginal cytology screening is not indicated, since the incidence of primary vaginal cancer is one to two cases per 100,000 women per year, much lower than that of cervical cancer.⁶⁵

However, before discontinuing screening, clinicians should verify that any Pap tests the patient had before the hysterectomy were all read as normal, that the hysterectomy specimen was normal, and that the cervix was completely removed during hysterectomy.

Be ready to explain the recommendations

It is very important for providers to understand the evidence supporting the latest guidelines, as many patients may not realize the significant technological improvements and improved understanding of the role of HPV in cervical cancer genesis that have resulted in the deferred onset of screening and the longer intervals between screenings. This knowledge gap for patients can result in anxiety when told they no longer need an annual Pap test or can start later, if the issue is not properly and thoroughly explained by a confident provider.

A FUTURE STRATEGY: HPV AS THE SOLE PRIMARY SCREENING TEST?

Since HPV testing is much more sensitive than Pap testing for detecting cervical lesions of grade CIN2 or higher, why not use HPV testing as the primary test and then do Pap testing (which is more specific) only if the HPV test is positive?

Mayrand et al⁴⁶ conducted the first large randomized trial in which HPV testing was compared directly as a stand-alone test with the Pap test in a North American population with access to quality care. Results were published in 2007. In Canada, a total of 10,154 women ages 30 to 69 years in Montreal and St. John’s were randomly assigned to undergo either conventional Pap testing or HPV testing. The sensitivity of HPV testing for CIN2 or CIN3 was 94.6%, whereas the sensitivity of Pap testing was only 55.4%. The specificity was 94.1% for HPV testing and 96.8% for Pap testing. In addition, HPV screening followed by Pap triage resulted in fewer referrals for colposcopy than did either test alone (1.1% vs 2.9% with Pap testing alone or 6.1% with HPV testing alone). In other words, HPV testing was almost 40% more sensitive and only 2.7% less specific than Pap testing in detecting cervical cancer precursors.

However, more controlled trials are needed to validate such a strategy. Furthermore, it remains unclear if a change from Pap testing to a primary HPV testing screening strategy will further reduce the mortality rate of cervical cancer, since the burden of cervical cancer worldwide lies in less-screened populations in low-resource settings.

Dillner et al,⁴⁸ in a 2008 European study, further demonstrated that HPV testing offers better long-term (6-year) predictive value for CIN3 or worse lesions than cytology does. These findings suggest that HPV testing, with its higher sensitivity and negative predictive value and its molecular focus on cervical carcinogenesis, may safely permit longer screening intervals in a low-risk population.

Sankaranarayanan et al⁷² performed a randomized trial in rural India in which 131,746 women age 30 to 59 years were randomly assigned to four groups: screening by HPV testing, screening by Pap testing, screening by visual inspection with acetic acid, and counseling only (the control group). At 8 years of follow-up, the numbers of cases of cervical cancer and of cervical cancer deaths were as follows:

• With HPV testing: 127 cases, 34 deaths
• With Pap testing: 152 cases, 54 deaths
• With visual inspection: 157 cases, 56 deaths
• With counseling only: 118 cases, 64 deaths.

The authors concluded that in a low-resource setting, a single round of HPV testing was associated with a significant reduction in the number of deaths from cervical cancer. Not only did the HPV testing group have a lower incidence of cancer-related deaths, there were no cancer deaths among the women in this group who tested negative for HPV. This is the first randomized trial to suggest that using HPV testing as the sole primary cervical cancer screening test may have a benefit in terms of the mortality rate.

At present, to the best of our knowledge, there are no US data validating the role of HPV testing as a stand-alone screening test for cervical cancer.

HPV VACCINATION DOES NOT MEAN THE END OF SCREENING

The development of an effective HPV vaccine and FDA approval of the first quadrivalent (active against HPV 6, 11, 16, and 18) recombinant vaccine (Gardasil) in 2006 has opened a new era of cervical cancer prevention.^73,74 At present, the Advisory Committee on Immunization Practices⁷⁵ recommends vaccination for females 9 to 26 years old.

However, HPV vaccination will not make screening obsolete, since not all women will be vaccinated, and those who have already contracted one of these high-risk HPV types will not benefit.^76,77 In addition, the current HPV vaccine does not protect against infection with other oncogenic HPV types. The experts estimate that the initial impact of the HPV vaccine on cervical cancer will not likely be apparent until at least 20 to 30 years after a nationwide vaccination program is implemented.^78,79 Therefore, the HPV vaccine certainly does not portend the end of screening. Vaccination combined with continued screening will provide added benefit for cervical cancer prevention.⁸⁰

The last decade has been an exciting period in the field of cervical cancer screening and prevention, with advances in technology, newly acquired knowledge, and the development of the HPV vaccine. As a result, our clinical practice has become a work in progress, continuing to evolve as we continue to discover more information. The possibility of eradicating cervical cancer has never been greater. The implementation of the most sensitive and effective screening strategy and of a worldwide HPV vaccination program will help us to eventually eradicate cervical cancer and make it a disease of the past.⁸¹

Cervical cancer screening and prevention have evolved rapidly in the last decade, especially in the 5 years since the introduction of the first cancer prevention vaccine, human papillomavirus (HPV) recombinant vaccine.¹

Providers need to understand the rationale for the recommendations so that they can explain them to patients. In particular, patients may wonder why we now begin screening for cervical cancer later than we used to, and why some women do not need to be screened as often. Both of these changes result from our enhanced understanding of the role of HPV in cervical cancer genesis.

In this article we will briefly review:

• The current understanding of the natural history of cervical cancer
• Advantages and disadvantages of cervical cytology, ie, the Papanicolaou (Pap) test
• The role of HPV testing in cervical cancer screening
• The latest screening guidelines (the new standard of care)
• A possible future screening strategy
• The impact of HPV vaccination on screening.

500,000 NEW CASES EVERY YEAR

The incidence of cervical cancer and its mortality rate have decreased more than 50% in the United States over the past 3 decades, largely as a result of screening with the Pap test.² In 2010, there were an estimated 12,200 new cases of invasive cervical cancer in the United States and 4,210 deaths from it,³ which are lower than the historical rates.

However, because most developing countries lack effective screening programs, cervical cancer remains the second-leading cause of death from cancer in women worldwide. According to a recent estimate, there are almost 500,000 new cases and 240,000 deaths from this disease worldwide every year.⁴ If effective global screening programs could be set up, they would markedly reduce the incidence of cervical cancer and deaths from it.⁵

HPV IS NECESSARY BUT NOT SUFFICIENT FOR CERVICAL CANCER TO DEVELOP

For cervical cancer to develop, the essential first step is infection of the cervical epithelium with one of the oncogenic (high-risk) types of HPV (see below).^6–10 Walboomers et al⁹ tested cervical tissue samples taken from 932 women with cervical cancer and detected HPV DNA in 930 (99.8%) of them.

Fortunately, most HPV-infected women do not develop cervical cancer, as most young women clear the infection in an average of 8 to 24 months.^11,12 However, if the infection persists, and if it is one of the high-risk types of HPV, precursor lesions can develop that can progress to cervical cancer.¹³ The evidence conclusively supports the association between oncogenic HPV infection and the subsequent development of virtually all cases of cervical cancer.^6–10

Known risk factors for HPV persistence and the subsequent development of high-grade lesions are cigarette smoking and a compromised immune system.^14,15

Terminology: Results of Pap smears

• Normal
• Atypical squamous cells of undetermined significance (ASC-US)
• Low-grade squamous intraepithelial lesions (LSIL)
• High-grade squamous intraepithelial lesions (HSIL)
• Cancer.

Terminology: Results of cervical biopsy

• Normal
• Cervical intraepithelial neoplasia grade 1 (CIN1)
• CIN2 (previously called moderate dysplasia)
• CIN3 (previously called severe dysplasia)
• Carcinoma in situ
• Invasive cervical cancer.

Lesions that are CIN2 or higher are considered high-grade.¹³

The 18 high-risk HPV types

More than 40 types of HPV infect the genital tract¹⁶; 18 of these (types 16, 18, 26, 31, 33, 35, 39, 45, 51, 52, 53, 56, 58, 59, 66, 68, 73, and 82) are classified as high-risk because of their causative association with cervical cancer (ie, their oncogenic potential).¹⁷

How HPV causes cervical cancer

In laboratory cultures, normal human cells die out after a few generations. However, if human epithelial cells are infected by one of the high-risk types of HPV, they can go on dividing indefinitely.^18,19

Two HPV proteins, E6 and E7, induce this cell “immortalization.”^20,21 E6 from high-risk HPV binds to the human tumor-suppressor protein p53 and rapidly degrades it in a proteolytic process. The p53 protein normally suppresses cell proliferation by arresting growth in the G1 phase of the cell cycle. Therefore, with less p53, the cell cannot suppress uncontrolled cell growth.^22–24

Similarly, E7 from high-risk HPV forms a complex with another human tumor suppressor, the retinoblastoma protein (pRB), and disrupts its binding to a transcriptional factor, E2F-1. The freed E2F-1 then stimulates DNA synthesis and uncontrolled cell growth.²⁵

Furthermore, HPV-16 E6 and E7 proteins can collectively cause cellular genetic instability.²⁶

The carcinogenic mechanism of high-risk HPV is complex. The host immune system and natural tumor suppression play important roles. However, the natural history of cervical intraepithelial neoplasia is not well understood. For example, it remains unclear if low-grade lesions such as CIN1 are necessary precursors to high-grade lesions and invasive cancer.^6,7,10

THE PAP TEST: SPECIFIC BUT NOT VERY SENSITIVE, AND PRONE TO ERROR

The principal advantage of cervical cytologic testing (ie, the Pap test) in detecting cervical dysplasia is its overall high specificity. Many studies have found that the specificity of conventional Pap testing can reach approximately 98%.²⁷

However, the conventional Pap test has drawbacks. Contaminants such as blood, discharge, and lubricant can make it difficult to interpret, and artifact can occur with air-drying of the Pap smear as it is transferred to the cell slide (“air-drying artifact”).

Liquid-based cytologic study has replaced the older method

To overcome these disadvantages, a liquid-based method of cervical cytologic study, ThinPrep (Hologic, Bedford, MA), was introduced in the mid-1990s. In this method, cell samples are first transferred to a liquid solution for mechanical separation from contaminants, and a representative sample of cells is then placed on a slide for review.

The liquid-based method filters out most contaminating blood, inflammatory cells, and debris. It also eliminates the air-drying artifact in the conventional Pap collection technique and improves specimen adequacy. Cytotechnologists find liquid-based specimens easier to read because the cells are more evenly distributed on a clearer background. Another advantage is that we can routinely test for HPV in the available residual specimen if the cytologic interpretation is abnormal.

The main disadvantages of the liquid-based method are that its specificity is lower than that of conventional Pap smears (around 78%) and that it costs more.²⁸ Nevertheless, the liquid-based technique has become the main method of cervical cytology, used by nearly 90% of gynecologists in the United States since 2003.¹

Cytology is still prone to false-negative results

Despite the success of both conventional Pap testing and liquid-based Pap testing, cervical cytology is inherently prone to sample-quality variation, subjective interpretation error, and false-negative results. False-negative results can be due to failure to transfer dysplastic cells to the slide or failure of the cytologist to recognize abnormal cells. In 30% of new cases of cervical cancer, the patient had recently had a Pap test that was interpreted as negative.^1,29

Errors in interpretation are exacerbated by inconsistency among cytopathologists. In one study,^6,30 when a group of quality-control pathologists reviewed nearly 5,000 cytology specimens, they came to the same conclusion that the original reviewers did more than 50% of the time only for negative and LSIL readings. Of the specimens initially reported as ASC-US, almost 40% were reclassified as negative on further review. Of those originally interpreted as HSIL, more than 50% were reclassified as LSIL, as ASC-US, or as negative.

Furthermore, many studies found that the sensitivity of conventional Pap testing was only around 50%.²⁷ The new liquid-based Pap test uses computer imaging, which has improved the rate of detection of cervical dysplasia but may still miss 15% to 35% of cases of HSIL (severe dysplasia) or cancer.³¹ Failure to detect cervical dysplasia or cancer on Pap smear has led to a number of lawsuits.³²

Clearly, with its relatively low sensitivity, cervical cytology is no longer good enough to use as a sole screening test in all situations. However, its high specificity is an advantage when it is combined with HPV testing in screening.

HPV TESTING AND PAP TESTING COMPLEMENT EACH OTHER

From 17% to 36% of HPV-infected women develop a cytologic abnormality within 5 years, compared with 4% to 15% of women who are HPV-negative.^33,34

The usefulness of testing for HPV in women who have had an abnormal Pap test has been well demonstrated in multiple studies.^35–38

The landmark Atypical Squamous Cells of Undetermined Significance/Low-Grade Squamous Intraepithelial Lesions Triage Study (ALTS)³⁹ found that 82.9% of women with LSIL were HPV-positive. The investigators concluded that HPV testing has little utility in women with LSIL, as the test would likely be positive and thus would not change the decision to perform colposcopy.

However, in women with ASC-US, the sensitivity of HPV testing for predicting CIN3 or cancer was 96.3% and the negative predictive value was 99.5%. In contrast, the sensitivity of a single repeat Pap test was only 44.1%. This large randomized trial conclusively validates the important role of HPV testing in triaging women with ASC-US.

More recently, a meta-analysis of 20 studies of HPV testing in women with ASC-US found that it had a sensitivity of 92.5% and a specificity of 62.5% for detecting CIN2 or worse lesions, and a sensitivity of 95.6% and a specificity of 59.2% for detecting CIN3 or worse lesions.⁴⁰

Furthermore, HPV testing in primary cervical cancer screening is strongly supported by large cross-sectional studies^41–45 and randomized clinical trials.^46,47 These studies have conclusively shown that HPV testing is significantly more sensitive than Pap testing for detecting cervical intraepithelial neoplasia, and that, when combined with Pap testing, it can achieve nearly 100% clinical sensitivity and nearly 93% specificity in women age 30 or older. Women who have negative results on both the HPV test and the Pap test can be reassured that their risk of undetected CIN2, CIN3, or cervical cancer is extremely low, since HPV testing has a negative predictive value close to 100%.⁴⁶

In large multinational European studies involving more than 24,000 women, the risk of CIN3 or cancer after 6 years of follow-up was only 0.28% in women who had negative results on both HPV and Pap testing at baseline. This rate was basically the same as in women who tested negative for HPV alone (0.27%). However, it was significantly lower than that of all women who had negative Pap test results (0.97%). The combination of HPV testing and Pap testing at 6-year intervals offered better protection than Pap testing alone at 3-year intervals.⁴⁸

NEW STANDARD OF CARE: THE LATEST SCREENING GUIDELINES

Until the mid-1990s, the strategy for cervical cancer screening had remained largely unchanged for many years. Since then, several advances have prompted changes in the standard of care.

1996—The US Food and Drug Administration (FDA) approved liquid-based Thin-Prep for cervical cancer screening, which improved specimen adequacy and reduced ambiguous interpretations compared with the original slide-based method of collection.⁴⁹