280 RISK OF COLORECTAL CANCER AFTER RESECTION OF ADENOMAS

V. Cottet1,2, V. Jooste V1,2, A. M. Bouvier1,2, J. Faivre1,2, C. Bonithon-Kopp1,3 1INSERM U866, DIJON, France, 2Registre Bourguignon des cancers digestifs, DIJON, France, 3INSERM CIE 1, CHU de Dijon, DIJON, France

Background: Colonoscopic removal of adenomas is recognized as the most efficient way to prevent colorectal cancer, although the actual benefit in routine clinical practice is yet poorly assessed. Objectives: The aim of this population-based study was to estimate the risk of colorectal cancer after adenoma removal in routine practice, in comparison with the general population. Methods: This study relies on the only population-based Registry which collects since 1976 all cases of polyps and colorectal cancer diagnosed in a well-defined administrative area in France. All patients residing in Coˆte-d’Or area (506,755 inhabitants), who were diagnosed with a first colorectal adenoma or carcinoma in situ between January 1990 and December 1999 were included and followed-up until the end-point date (December 2003). The observed numbers of cases of colorectal cancer among the study population were compared with the expected numbers calculated on the basis of age- and gender- specific rates in the general population using data from the Burgundy Registry of Digestive Cancers. The ratio of observed to expected cases was reported as a standardized incidence ratios (SIR). Results: A total of 5,782 adenoma patients were included and 88 colorectal cancers were detected during a follow-up of 39,730 persons-years. The expected number of colorectal cancers in this population was 69. In comparison with the general population, the risk of colorectal cancer after firstadenoma removal was significantly increased (SIR = 1.28 [Confidence Intervals 95%: 1.02–1.57]), especially for advanced adenomas (SIR = 2.11 [CI 95%: 1.61–2.73]). Removal of non-advanced lesions was associated with a slightly decrease in the incidence of colorectal cancer (SIR = 0.71 [CI 95%: 0.47–1.01]). Conclusion: In actual conditions of clinical practice, the risk of developing colorectal cancer after adenoma removal remained greater than in the general population. Both the high individual carcinogenetic risk and shortcomings in follow-up probably contribute to these findings.