Objective: To identify factors influencing the occurrence of cancer in the rectal remnant in patients with familial adenomatous polyposis (FAP) after colectomy and ileoreotal anastomosis (IRA). Summary Background Data: The risk for rectal cancer in patients with FAP after colectomy and IRA remains a major concern. Methods: Between 1955 and 1997, 371 patients (206 men, 165 women) from the Registry of Hereditary Colorectal Tumors underwent colectomy and IRA as a primary surgical procedure. Survival was estimated using the Kaplan-Meier method. Cox proportional hazard models were fitted to assess the relative excess risk of rectal cancer and to control for confounding factors. A multivariate analysis was performed to assess the relation between cancer risk in the rectum and sex, age, number of rectal polyps, colon cancer, and APC germline mutation. Results: Median follow-up was 81 months. Eighty-nine patients (24%) had colon cancer at the time of surgery. The APC mutation was found in 200 patients. In 27 patients, cancer developed in the retained rectum 1 to 26 years after surgery. The incidence of rectal carcinoma appears to increase with time: at 10, 15, and 20 years after surgery, the cumulative risk was 7.7%, 13.1%, and 23.0%, respectively. Multivariate analysis identified as independent predictors the presence of colon cancer at IRA and a mutation occurring between codons 1250 and 1464; both factors increased the risk nine times. Conclusions: The presence of cancer at IRA and APC mutation type are the most important risk factors for the future development of cancer in the rectal remnant in patients with FAP.
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