Follow-up of a negative sigmoidoscopic screening exam at 3 years rather than the currently recommended 5-year interval may detect additional cases of advanced colon polyps and colon cancers, according to an article in the July 2nd issue of The Journal of the American Medical Association.

Robert E. Schoen, M.D., M.P.H., and his American colleagues examined the number of adenomas and cancerous lesions in the distal colon found by repeat flexible sigmoidoscopic examination 3 years after a negative result. Participants were drawn from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, a randomized controlled community-based study of cancer screening. Average age was 65.7 years at study entry (1993 to 1995), and 61.6 percent were men. Individuals underwent screening with flexible sigmoidoscopy at baseline and at 3 years. Of 11,583 people eligible for repeat screening 3 years after an initial negative examination, 9,317 (80.4 percent) returned.

The researchers found that a total of 1,292 returning participants (13.9 percent) had a polyp or mass detected by the 3-year follow-up examination. The authors wrote, "In the distal colon, 3.1 percent (292 of 9,317) were found to have an adenoma or cancer. The incidence of advanced adenoma (72 patients) or cancer (6 patients) in the distal colon was 0.8 percent (78 of 9,317). Of individuals with advanced distal adenomas detected at the year 3 examination, 80.6 percent (58 of 72) had lesions found in a portion of the colon that had been adequately examined at the initial sigmoidoscopy."

"… our results show that 3 years after a negative flexible sigmoidoscopy examination, there is a 0.8 percent incidence of advanced adenomas or cancer detectable in the distal colon. Although the overall percentage with detected abnormalities is modest, these data raise concern about the impact of a prolonged screening interval after a negative examination," the authors concluded.

In an accompanying editorial, Robert H. Fletcher, M.D., M.Sc., wrote that all screening tests are imperfect: "They can improve patients' chances of a good outcome but cannot guarantee it. Screening tests are chosen because they are easier, safer, and less expensive than definitive tests, but at the cost of missing some cancers and sounding many false alarms. Perhaps clinicians and patients tend to expect colorectal cancer screening to be more effective than it really is because some of the same tests (sigmoidoscopy and colonoscopy) are used for both screening and diagnosis."

"In the quest for better ways to screen, clinicians should not overreact, pressing sigmoidoscopy beyond what it can reasonably do. While the results of the study by Schoen et al, as sound as they are, are not sufficient to prompt change in the currently recommended screening interval of 5 years, the findings do reveal much more about the consequences of this screening interval for cancer prevention than was known before," Dr. Fletcher added.