FECAL OCCULT BLOOD SCREENING FOR COLORECTAL-CANCER - IS MORTALITY REDUCED BY CHANCE SELECTION FOR SCREENING COLONOSCOPY

Annual fecal occult blood test (FOBT) screening using rehydrated Hemoc cult slides has been reported in the Minnesota Colon Cancer Control St udy to reduce colorectal cancer mortality by about 33%. However, some of the benefit of FOBT screening may come from ''chance'' selection of persons for colonoscopic examination because of the high positivity r ate of FOBT (about 1 0%) that may occur for reasons other than a bleed ing cancer or polyp. To determine how much this mechanism could accoun t for the benefit of FOBT screening, we used a simple mathematical mod el to simulate the course of a cohort of screened persons, incorporati ng published data including those f rom the Minnesota study. The resul ts suggest that one third to one half of the mortality reduction obser ved from FOBT screening in the Minnesota study may be attributable to chance selection for colonoscopy. We conclude that annual FOBT screeni ng with rehydration is a haphazard method for selecting persons for co lonoscopy.