Colorectal polyp counts and cancer risk in familial adenomatous polyposis.

Abstract

In familial adenomatous polyposis, colorectal cancer prevention is by prophylactic colectomy, but dietary or chemopreventative strategies have been recently proposed in low-risk individuals. The aim of this study was to define predictive risk factors for colorectal cancer in familial adenomatous polyposis. Between 1918 and 1993, 317 patients underwent colectomy. A multivariate analysis was performed to assess the relationship between colorectal cancer risk and polyp count, sex, and age at colectomy. The median polyp count was 842 (range, 78-7500), and cancer was found in 22% of patients. Polyp count and age, but not sex, predicted cancer risk. Patients with >1000 polyps had 2.3 times greater risk of cancer than those with <1000 polyps (P=0.006). Synchronous cancers increased with poly count (P<0.05). Each 10-year age group had a 2.4-fold difference in cancer risk (95% confidence interval, 1.9-3.2; P<0.001). Four cases of cancer occurred in patients at low risk (younger than 30 years of age, <1000 polyps; 3.3%). More adenomas and older age are associated with a higher risk of colorectal cancer. However, cancer does occur in low-risk individuals and may be missed by surveillance, making alternatives to prophylactic surgery inadvisable.