METACHRONOUS COLON-CANCER IN PERSONS WHO HAVE HAD A LARGE ADENOMATOUSPOLYP

Objective: To determine, among persons who have had a large colon poly p, the risk of subsequent colon cancer at a site distant from that pol yp, Methods: Follow-up was done for 226 persons at the Mayo Clinic who had had a greater than or equal to 1-cm polyp demonstrated on barium enema between 1965 and 1970 and for whom yearly colon surveillance exa mination was recommended, Information was collected from Mayo Clinic r ecords and from contact with patients, physicians, and other hospitals regarding the results of surveillance examinations and the developmen t of colon cancer, Colon surveillance was routinely done at the Mayo C linic using the technique of single contrast barium enema with vigorou s manual fluoroscopic examination and proctoscopy. The expected rate o f colorectal cancer (CRC) was calculated based on previously published rates for this community, Results: Patients received, on average, fou r colon examinations in addition to the examination that discovered th e index polyp, During 2126 person-years of follow-up, 16 persons devel oped a colon cancer at a location other than the site of the index pol yp, in comparison with 4.0 expected cases, for a standardized incidenc e ratio of 4.0 (95% CI, 2.3, 6.4), The cancers were large (mean 4.5 cm ) at presentation, and eight of the 16 cancers had been preceded withi n 3 yr by at least one negative barium enema, Conclusions: The rate to develop colon cancer in persons who have had a large colon polyp is a bout 4 times the expected rate, suggesting that such persons should be considered for aggressive colonoscopic surveillance, The failure to d etect early cancer or its precursors by surveillance barium enema is p robably explained by inherent insensitivity of single contrast barium enema.