Small adenomas detected during fecal occult blood test screening for colorectal cancer. The impact of serendipity.

Yearly fecal occult blood testing (FOBT) has been recommended for men and women over age 50 years as part of a screening regimen intended to reduce colorectal cancer mortality. The primary targets of screening are early, surgically curable colon cancers and large adenomatous colon polyps; however, screening may sometimes reveal only small adenomas (ie, less than 1 cm in diameter). To assess the rates and mechanisms of FOBT detection of small adenomas, we performed quantitative analyses utilizing estimates of adenoma bleeding rates and FOBT sensitivity and specificity. The analysis suggests that the mechanisms of detection of small adenomas is often chance or serendipity. This occurs when an FOBT result is "falsely" positive because of diet or non-neoplastic gastrointestinal bleeding and leads to colonoscopic discovery of a nonbleeding small adenoma. Nevertheless, small adenomas remain undetected in most persons who have them, even if repeated yearly FOBT screening is done. The identification of persons with small adenomas should not be assumed to be an important beneficial outcome of FOBT screening, because the clinical significance of small adenomas is not clear, the mechanism of detection is serendipity, and only a minority of persons with small adenomas are identified. The current recommendations to perform periodic surveillance colonoscopy following removal of small adenomas detected during FOBT screening should be reexamined.