Impact of a family history of colorectal cancer on the prevalence of advanced adenomas of the rectosigmoid colon at flexible sigmoidoscopy in 3147 asymptomatic patients.

Flexible sigmoidoscopy is advised as a screening test for colorectal cancer for persons with a family history of late-onset colorectal cancer. The expected outcome for this approach is not well established. We designed a large, prospective study of an unselected population to assess the impact of a family history of one first-degree relative with colorectal cancer on the prevalence of advanced adenomas at screening flexible sigmoidoscopy. We evaluated 8121 patients referred for flexible sigmoidoscopy between 1997 and 1999 and 3147 patients met the inclusion criteria. The 3147 patients were divided into 210 with a family history of colorectal cancer and 2937 without a family history and analyzed for differences in the prevalence of advanced adenomas. Of the 210 with a family history, 3 had an advanced adenoma of the rectosigmoid colon (1.4%) Of the 2937 without a family history, 52 had an advanced adenoma of the rectosigmoid colon (1.8%), including 2 cancers. These differences were not significant. In conclusion, a family history of colorectal cancer had no impact on the prevalence of advanced adenomas in asymptomatic patients at screening flexible sigmoidoscopy. The prevalence rates for advanced adenomas and carcinomas of the rectosigmoid colon were low.