Not so fast ...
Arguing the case against a lowering of the starting age, Dr. Weinberg agreed with Dr. Ladabaum that colon cancer risk for younger people is rising.
That risk has increased from 5.9/100,000 to 7.2/100,000, which is a relative increase of 22%, he noted.
“That is what newspapers will want to put on their headlines to sensationalize it – that the risk of colon cancer for young people is up by over 20%,” said Dr. Weinberg. “But that represents an absolute risk of just 1.3 more people/100,000. Put in some context, 99.9% of people in their 40s will not develop colon cancer.”
This observation was not to “make light of the remainder,” he emphasized, but “the overwhelming majority are not going to get this disease at this age,” he noted.
“It’s also not entirely clear that starting screening at 45 is the right answer,” he added.
“Taken to a somewhat ridiculous extreme,” he continued, “why not start at 40? You’ll catch more people that way, but no one is advocating that.”
A better understanding of the factors contributing to the increased CRC incidence seen in younger adults is very important, he argued, and he suggested that some of it may occur because of screening, along with factors such as obesity, diabetes, and childhood exposures.
Modeling has been done to calculate the risk and benefit of early screening, but while useful for decision making, models are “usually wrong and sit near the bottom of the evidence hierarchy.”
“Models help inform decisions, but they don’t define the standard of care,” Dr. Weinberg said. “No one would vaccinate a population based on a model.”
Dr. Weinberg also emphasized that the new recommendation from the American Cancer Society to start screening at age 45 years is qualified. This means that while “clear evidence of benefit exists,” so does uncertainty about whether “the benefits really outweigh the harms.”
The current evidence for reducing the screening age is not yet clear, he believes, and he questioned the premise that age should be the only criteria for cancer stratification.
Dr. Weinberg cited one study that looked at early-onset colon cancer (ages 18-49 years) and compared it with two groups: patients diagnosed at 50 years and older and matched controls (Clin Gastroenterol Hepatol. 2019;S1542-3565[19]31108-5). Besides age, the study authors identified several nonmodifiable risk factors that were associated with early-onset disease, including sex, race, history of inflammatory bowel disease (IBD), and family history of colorectal cancer.
“Being male was a risk factor and having a family history increased your risk by three times,” said Dr. Weinberg. “And I would note that this study had removed people, at least as best one can, who were known to have syndromic risks of early-onset colon cancer (such as familial adenomatous polyposis.”
Earlier screening (by age 40 years) should already be taking place in people with such syndromes, he commented, as well as those with a known family history and IBD. “Those recommendations were there before the ACS, and we don’t necessarily need another one,” he added.
To make things a little more confusing, a second recent study, using National Cancer Data Base data from 2004 to 2015, identified another set of factors associated with colon cancer in younger adults (Cancer. 2019 Nov 1;125:3828-35). This study showed diagnosis younger than 50 years rose only in non-Hispanic white men, in Hispanic and non-Hispanic white women, and in those living in urban vs. rural areas.
“But it gets more interesting,” Dr. Weinberg pointed out. “Risk increased over time for people in the highest zip code income quartile and those with private insurance, and risk was lower for people with Medicaid and no insurance at all,” he noted. “Well, that smacks of access to me,” he commented.
Another issue is the possibility of lead-time bias. During 1975-2015, incidence rose over time, according to Surveillance, Epidemiology, and End Results data (J Natl Cancer Inst. 2017 Aug;109:djw322). Screening of persons younger than age 49 years also more than doubled, from a low level in 2000 of about 6% to more than 15% by 2010. As screening increases, the incidence increases, Dr. Weinberg pointed out. “But mortality doesn’t change. And despite what Dr. Ladabaum said a moment ago about lead-time bias, that is textbook lead-time bias in any epidemiology study.”
Finally, it is essential to carefully weigh the benefit against the risk, Dr. Weinberg said.
A core principle of population screening is to create more future health benefits than harms, and if the screening age is lowered, several million additional colonoscopies will be performed.
Colonoscopy reduces the colorectal cancer mortality risk by about 75%, and the incidence of the disease is 7.2/100,000 in the younger age group. But colonoscopy-specific mortality – just having the test – is associated with a death rate of 7/100,000,” Dr. Weinberg pointed out. “Let’s not forget that there is a risk associated with this procedure.” (Gastrointest Endosc. 2011 Oct;74:745-52).
Dr. Weinberg emphasized that everyone wants to reduce the burden of cancer, and models are helpful for that purpose. “They’re obviously thought provoking, but they’re not adequate to drive change without additional evidence of clinical and cost-effectiveness,” he said. “These are important questions that need better data.”
He added that without changing the current screening protocol, “we could certainly emphasize more than ever the impact of family history and IBD on colon cancer risk and colon cancer prevention.”
“And certainly, there’s plenty of evidence that patients with a known family history of colon cancer are not getting screened at the right age or with the right frequency,” Dr. Weinberg concluded. “We can do better. All of us can do better.”
Dr. Weinberg has disclosed relationships with Fujifilm and Exact Sciences. Dr. Ladabaum has disclosed relationships with Lean Medical, Universal Dx, Clinical Genomics, Medtronic, Modus GI, and Quorum Consulting.
This article first appeared on Medscape.com.