Background
Lung cancer is the leading cause of cancer death among men and women in the United States and will account for an estimated 160,000 deaths in 2012. The average 5-year survival for lung cancer is approximately 16%, among the poorest of all cancers. Studies have not shown a significant decrease in lung cancer mortality using chest x-ray (CXR) with and without sputum cytology.
However, the American Cancer Society recently published guidelines for lung cancer screening based on additional data from the National Lung Screening Trial (NLST), which reviewed the utility of low-dose computed tomography (LD-CT) for lung cancer screening.
A survey of 962 primary care physicians in 2006-2007 found that 25% of those surveyed believed that one or more of the national expert groups recommend screening asymptomatic patients for lung cancer. More than 50% of those surveyed had ordered a CXR, and nearly 25% had ordered LD-CT for lung cancer screening of asymptomatic patients in the last 12 months.
Conclusions
NLST randomized patients to annual LD-CT vs. annual CXR over 3 years, with results showing a 20% reduction in cancer death and a 6.7% reduction in death from all causes in the LD-CT arm. Two other randomized, controlled trials using the same endpoints but shorter follow-up were unable to demonstrate this same reduction.
Limitations and harms associated with LD-CT include the psychological stress and anxiety associated with abnormal results, false-positive test results, incidental findings outside of the lung, and morbidity/mortality associated with further diagnostic evaluations in patients with and without lung cancer.
A total of 39% of individuals experienced at least one abnormal CT scan over the 3 years of screening, and most of these patients needed additional imaging to determine the significance of the identified abnormalities. A total of 2.7% of patients ultimately found not have lung cancer underwent invasive procedures for further evaluation, with a complication rate of 0.06%. This is in comparison to the 11.2% complication rate for invasive procedures in patients who were subsequently diagnosed with lung cancer. Radiation exposure was not reported.
A total of 7.5% of participants were found to have incidental findings outside the lung fields on their screening imaging. Currently, there is insufficient evidence to evaluate the potential for overdiagnosis of lung cancer with LD-CT.
The average NLST participant was 62 years old, with approximately a 50-pack-year smoking history. The NLST conclusions suggests LD-CT screening is beneficial in men and women aged 55-74 years who are in reasonably good health, are current smokers or former smokers having quit within the past 15 years, and have a 30 or more pack-year smoking history.
Several studies have shown evidence of higher rates of smoking cessation in patients who have chosen to participate in lung cancer screening programs using LD-CT. A community-based screening program for oral, head, and neck cancer showed some increase in smoking cessation, but other programs targeting lung cancer screening have not replicated this data.
Few insurance programs provide coverage for LD-CT performed for lung cancer screening.
Implementation
The American Cancer Society lung cancer screening guidelines recommend that clinicians initiate a discussion about lung cancer screening with their patients aged 55-74 years who are in reasonably good health, are current smokers or former smokers who quit within the past 15 years, and have a 30 or more pack-year smoking history. Adults who choose to be screened should have annual LD-CT imaging until the age of 74 years.
Adults who choose to undergo lung cancer screening by LD-CT should be referred to an organized screening program. If such a program is not available, then referral should be made to a center that performs a reasonably high volume of CT scans, diagnostics tests, and lung cancer cases. If this is not available, or if the patient is unwilling to travel to a location where this is possible, then screening is not recommended.
Smoking cessation must remain a highest priority for all patients who are currently smoking. LD-CT screening should not be seen as an alternative to smoking cessation.
The American College of Chest Physicians, the American Society of Clinical Oncology, and the American Lung Association also suggest LD-CT screening based on similar NLST criteria.
The National Comprehensive Cancer Network recommends annual LD-CT for persons who meet NSLT entry criteria and for individuals 50 years or older with a smoking history of 20 or more pack-years who have one additional known risk factor for lung cancer.
The American Association for Thoracic Surgery recommends annual lung cancer screening with LD-CT for adults aged 55-79 years with a 30 pack-year history of smoking, annual screening beginning at age 50 years for adults with a 20-pack-year history and an additional calculated cumulative 5-year risk of developing lung cancer of 5% or greater. The 5-year cumulative risk is in conformity with the U.K. Lung Cancer Screening Trial, which uses the Liverpool Lung Project to calculate risk.