Stool-based screening tests and lower endoscopy reduce the rate of mortality from colorectal cancer, concluded the World Health Organization’s International Agency for Research on Cancer (IARC).
In a special report in the New England Journal of Medicine, the IARC summarized its evaluation of colorectal cancer screening methods and outcomes using published evidence gathered from randomized, controlled trials, observational studies, and modeling studies. Screening tests included in the evaluation were stool-based, endoscopic, and computed tomography (CT) colonography-based methods. Outcomes and the benefit-to-harm balance were considered in average-risk populations.
Stool-based tests for occult blood
Studies of guaiac testing provide “sufficient evidence that screening every 2 years with the guaiac test without rehydration reduces colorectal cancer mortality, as does screening every 1 or 2 years with the higher-sensitivity guaiac test,” the IARC members wrote. However, the review found no evidence that screening every 2 years with the guaiac test without rehydration reduces the incidence of colorectal cancer.
Evidence from observational studies and inferences drawn from randomized trials showed consistently that screening every 2 years with the fecal immunochemical test (FIT), a more sensitive method than guaiac testing, reduces the rate of colorectal cancer mortality. FIT also performed better than guaiac testing for detecting advanced adenoma and colorectal cancer.
Overall, the benefits of stool-based tests outweigh the potential harms, the panel concluded. It referred to modeling studies in which “all stool-based tests for occult blood provided gains in quality-adjusted life-years, as compared with no screening, especially FIT and higher-sensitivity guaiac testing.”
Among endoscopic methods, sigmoidoscopy significantly reduced the relative risk of death from colorectal cancer by 22% to 31% in three of four large randomized studies examined. In a recent meta-analysis, screening colonoscopy was associated with reductions in both the incidence of colorectal cancer and death from colorectal cancer by almost 70%. The same meta-analysis demonstrated reductions in both incidence of and death from colorectal cancer by almost 50% with screening sigmoidoscopy.
Both stool-based tests and sigmoidoscopy can generate psychological harms and unnecessary referrals for positive results. Colonoscopy causes bleeding and perforation in 0.01% to 0.05% of procedures. Despite this, the IARC panel members agreed that the benefits of a single screening sigmoidoscopy or colonoscopy outweighed the harms, and both provide gains in quality-adjusted life-years compared with no screening.
The value of CT colonography was more difficult to assess given the lack of published, randomized clinical trials of its effect on colorectal cancer incidence and mortality. In tandem studies, in which the same participants were screened sequentially with both CT colonography and colonoscopy, the detection rates of advanced neoplasias were similar between the two methods, the panel found.
CT colonography is associated with radiation-induced effects, and a positive screening test is followed by colonoscopy and its potential harms. Extracolonic findings are also possible.
“On the basis of these data, there is limited evidence that a single screening with CT colonography reduces colorectal cancer incidence or mortality,” the panel wrote. It added that the evidence is inadequate that the benefits of a single round of screening with CT colonography outweigh the harms.
The panel concluded that among all screening techniques, stool-based tests and lower endoscopy not only reduce the risk of death from colorectal cancer, but their benefits outweigh their harms. The evidence was insufficient for the panel to conclude that any one screening method is more effective than another.
Among the limitations of the review, the panel cited that most of the studies reviewed “had been conducted in settings with middle or high incomes, in which the incidence of colorectal cancer is generally high; in asymptomatic, average-risk populations; and under conditions in which colorectal cancer screening, including subsequent follow-up and treatment, can be delivered with high quality.”
This report was supported by the American Cancer Society and the Centers for Disease Control and Prevention.