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Incidence of Advanced Adenomas and Distal Cancers After Negative Screening Sigmoidoscopy

Researchers examined the yield of repeat sigmoidoscopy 3 years after an initial negative exam.

Current guidelines for colorectal cancer screening recommend flexible sigmoidoscopy every 5 years. The randomized, controlled Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial includes an evaluation of sigmoidoscopy screening for colorectal cancer. Individuals randomized to the intervention group who have initial negative sigmoidoscopy examination are advised to undergo repeat examination 3 years after the initial exam. In this report, investigators describe 9317 participants (80% of the eligible cohort) who underwent repeat flexible sigmoidoscopy 3 years after an initial negative exam.

The incidence of adenoma or cancer in the distal colon was 3.1%. The incidence of advanced adenoma (72 patients) and cancer (6 patients) in the distal colon was 0.8%. The authors classified incident lesions identified at the repeat exam as: (1) not likely to have been reached during the initial examination, (2) associated with poor preparation during the initial examination, or (3) detectable (but not found) at the initial examination. About 80% (58 of 72) of incident advanced lesions that were identified at the repeat exam were located in a part of the colon that had been adequately examined at the initial sigmoidoscopy. On the basis of this finding, the authors challenge the appropriateness of a long interval between exams after a negative screening exam.

Comment: An accompanying editorial urges clinicians not to overreact to these results. I agree, particularly since there already is substantial evidence indicating that lower bowel endoscopic examinations are not perfectly protective against the development of colorectal cancer. It is important for clinicians and the public to recognize that none of the current colorectal cancer screening measures is perfectly effective, but that several are as good or better in reducing cancer mortality than other accepted types of screening tests. Decreasing the interval between examinations will reduce cost-effectiveness, increase risk, and result in uncertain benefits. It would be useful to know whether the incidence of advanced lesions identified in this study at the repeat exam differed between centers. Such information would help to clarify whether the less-than-perfect protection of sigmoidoscopy reflected poor quality exams at certain centers (and not the potential of sigmoidoscopy when optimally performed) or whether it reflected phenomena such as flat lesions or tumors with different biologic behavior (e.g., fast growth rates).

— Douglas K. Rex, MD

Published in Journal Watch Gastroenterology August 26, 2003

Citation(s):

Schoen RE et al. Results of repeat sigmoidoscopy 3 years after a negative examination. JAMA 2003 Jul 2; 290:41-8.

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Fletcher RH. Screening sigmoidoscopy -- How often and how good? JAMA 2003 Jul 2; 290:106-8.

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• Medline abstract (Free)