Atkin, Wendy Sheila; (1991) Risk of subsequent colon and rectal cancer after removal of adenomas from the rectosigmoid. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

As a cancer prevention measure, surveillance by repeated colonoscopy is currently recommended for all patients found to have colorectal adenomas. In order to assess the long-term risk of colorectal cancer after polypectomy, a detailed examination was undertaken of 1618 patients (1061 men and 557 women) with rectosigmoid adenomas excised between 1957 and 1980 who did not have such colon surveillance. A total of 23,015 years of follow-up (mean 14.2 years per person) were accrued. Overall, the incidence of rectal cancer was similar to that in the general population (standardized incidence ratio=1.24; 95% confidence interval: 0.7- 2.1). However most rectal cancers developed in patients with large (? 1cm), tubulovillous, villous or severely dysplastic adenomas which had been incompletely excised without follow-up to monitor for local recurrence. This occurred more frequently in the women leading to significant sex- differences in risk. Risk of colon cancer was twice that in the general population in both men and women. Risk depended on the size, histologic type and, to a lesser extent, the number of adenomas in the rectosigmoid. For 842 patients with either tubulovillous, villous or large (>1 cm) adenomas, the standardized incidence ratio was 3.6 (95% confidence interval: 2.4-5.0). For the remaining 776 patients having with only small (<1cm), tubular adenomas, the standardized incidence ratio was 0.5 (95% confidence interval: 0.1-1.3). Patients with only small tubular adenomas were therefore considered to be at low risk and the remainder at high risk. The number of adenomas found in the rectosigmoid did not influence the division into risk groups. The risk of development of synchronous and metachronous adenomas in the colon was of the order of 20% to 40% in both low and high risk groups, but the adenomas in the low risk group were mainly small (< 1cm). These results suggest that endoscopic surveillance for patients with only small, mildly or moderately dysplastic, tubular adenomas may not be rewarding as a cancer prevention measure since the risk of colorectal cancer is low. Colonoscopic surveillance would probably benefit the remaining high risk group, although assessment of the degree of benefit is beyond the scope of this study.

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