[The role of epidemiologic research of the natural history of cancer for evaluating cancer screening programs--a prospective study of colorectal polyps on the occurrence of colorectal cancer].

: In order to elucidate the natural history of colorectal polyps and to examine the effectiveness of endoscopic polypectomy in reducing the incidence of colorectal cancer, we conducted a retrospective cohort study of all patients who had undergone endoscopic examination at the Center for Adult Diseases, Osaka in 1970-82. The study subjects consist of 653 non-polyp cases and 431 colorectal polyp cases including 222 cases treated by endoscopic polypectomy. These were followed up until the end of 1985 by the method of a record linkage with the Osaka Cancer Registry's file. The colorectal polyp group and the endoscopic polypectomy group experienced 4.4 and 2.9 times, respectively, as much incidence of colorectal cancer as the non-polyp group. The magnitude of the prevented fraction by the use of endoscopic polypectomy was estimated at 31.3%. A large-scale and long-term study is necessary to elucidate the original study purpose.