Clinical impact of colonoscopic screening in first-degree relatives of patients with hereditary non-polyposis colorectal cancer.

Sixty-one asymptomatic individuals with an affected first-degree relative from five large hereditary non-polyposis colorectal cancer (HNPCC) kindreds were screened by colonoscopy. Neoplasms were found in nine (15 per cent) of 61 individuals on the first screen. Five subjects had a single adenoma while two had two adenomas each. There were two patients (3 per cent) with malignant neoplasms: one with a Dukes B adenocarcinoma and one with synchronous Dukes C adenocarcinomas in the caecum and ascending colon. These findings support the hypothesis that adenomas do not occur in large numbers in HNPCC families but, because of the high malignant conversion rate, biennial colonoscopy with removal of polyps seen is recommended.