Screening asymptomatic patients at high risk for colon cancer with full colonoscopy.

To evaluate the reliability of screening only the distal colon in patients at high risk for colonic cancer, the endoscopic findings of 49 completely asymptomatic patients who underwent colonoscopy based solely on a positive family history of colonic cancer (average age, 54.5 years) were reviewed. Polypoid lesions were present in 31 (63.3 percent). Thirty-three polyps in 13 patients were larger than 1 cm, including two invasive cancers. Eleven patients (22.4 percent) had polyps proximal to 40 cm only and would not have been identified on examination of the distal bowel alone. The predictive accuracy of rectosigmoid screening in this population is 78 percent. Initial screening of patients at high risk for colonic cancer should include full colonoscopy. The extent of follow-up examinations is then based on endoscopic findings.