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The first study to demonstrate convincingly that endoscopic screening and removal of precancerous lesions prevents colorectal cancer was a U.S. case-control study of sigmoidoscopy, which showed a 60% reduction in risk for colorectal cancer mortality from distal colon cancers following proctosigmoidoscopy (N Engl J Med 1992; 326:653). This protective effect lasted for at least 10 years. Subsequently, another case-control study, primarily of flexible sigmoidoscopy, showed an 80% reduction in distal colon cancers and an effect duration of at least 16 years (Journal Watch Gastroenterology Jul 29 2003). Neither group could exclude a longer duration of effect.
German investigators have performed a similar study of screening colonoscopy. They ident…