Is flexible sigmoidoscopy best for colorectal cancer screening?

Reuters Health Information: Is flexible sigmoidoscopy best for colorectal cancer screening?

Is flexible sigmoidoscopy best for colorectal cancer screening?

Last Updated: 2017-08-21

By Megan Brooks

NEW YORK (Reuters Health) - A re-analysis of 2016 data from the U.S. Preventive Services Task Force (USPSTF) on colorectal cancer (CRC) screening indicates that flexible sigmoidoscopy reduces the risk of death, researchers say.

"More than 50 years after the announcement of the first clinical trial of cancer screening, a screening method has shown a reduction in the risk for death compared with no screening. If the primary goal of screening is to reduce the risk for death, then the evidence supporting flexible sigmoidoscopy is substantially stronger than that of other screening methods," the study team said online August 21 in Annals of Internal Medicine.

Last year, the USPSTF concluded that CRC screening substantially reduces disease-related mortality, but it did not recommend any one screening approach over another. It also concluded that no method of screening for CRC reduces all-cause mortality in any age group. (

Dr. Andrew Swartz, from the Yukon-Kuskokwim Delta Regional Hospital in Bethel, Alaska, and colleagues at University of South Carolina in Columbia, write in their new paper that the panel's conclusion was partially based on a meta-analysis of four randomized trials that compared flexible sigmoidoscopy screening with no screening. The meta-analysis combined results from the two age cohorts of the Norwegian Colorectal Cancer Prevention study (NORCCAP) as if these cohorts were a single trial.

This, they argue, created a "Simpson paradox that obscured the reduction in all-cause mortality by changing 2 statistically nonsignificant reductions into a statistically significant increase. This effect was large enough to nullify the reductions in all-cause mortality of the other trials in the meta-analysis."

In their re-analysis, Dr. Swartz and colleagues found that screening with flexible sigmoidoscopy does reduce all-cause mortality with an absolute risk reduction that is "clinically important" relative to other methods.

Using the assumed risk for death in the U.S. population of screening age, they report an absolute risk reduction of 3.0 deaths per 1000 persons invited to screening after 11.5 years of follow-up.

On the basis of their re-analysis, the researchers believe that CRC screening guidelines "warrant reassessment to incorporate this evidence."

In email to Reuters Health, Dr. Swartz noted that screening with flexible sigmoidoscopy has "fallen into disuse in the U.S., but the results of this study indicate that our current practice warrants reassessment. In clinical trials, flexible sigmoidoscopy is the first cancer screening method to show a decreased risk of death compared to not screening. Alternative colorectal cancer screening methods have either failed to reduce the risk of dying or have not been evaluated in clinical trials. The main message for policy makers is that the USPSTF guidelines should be reassessed."

"We should reconsider using flexible sigmoidoscopy as our primary method of screening for colorectal cancer," Dr. Swartz wrote.

Asked for comment, general internist Dr. Doug Owens, USPSTF vice chair and associate director of the Center for Innovation to Implementation at the Veterans Affairs Palo Alto Health Care System in California, told Reuters Health by email, "The Task Force last looked at screening for colorectal cancer in 2016, so it is not yet in the process of updating this recommendation. The Task Force looks forward to reviewing all relevant evidence when it updates its review in the future."

The complete USPSTF recommendation statement on CRC screening is available here:


Ann Intern Med 2017.

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