Screening for Colorectal Cancer Using Colonoscopy

The first study to clearly demonstrate the efficacy of colorectal cancer screening was a case-control study published in 1992, which found a 60% reduction in distal colorectal cancer mortality associated with sigmoidoscopy [1]. Subsequently, casecontrol studies at the Marshfield Clinic in Wisconsin [2] and in Washington State [3] demonstrated that flexible sigmoidoscopy was associated with an 80% reduction in distal colorectal cancer incidence. In addition, evaluation of a randomized controlled trial of fecal occult blood testing demonstrated that fecal occult blood testing had resulted in not only a reduction in colorectal cancer mortality but also in a 20% reduction in incidence of colorectal cancer [4]. The latter appeared related to identification of large colorectal polyps by fecal occult blood testing and their subsequent removal by colonoscopy and polypectomy. In 1993, evaluation of an adenoma cohort participating in the National Polyp Study reported that colonoscopy and polypectomy was associated with a 76–90% reduction in the incidence of colorectal cancer by comparison of incident cancer rates in the adenoma cohort compared to expected rates in three reference populations [5].