Genotype and phenotype factors as determinants for rectal stump cancer in patients with familial adenomatous polyposis

Objective To identify factors influencing the occurrence of cancer in the rectal remnant in patients with familial adenomatous polyposis (FAP) after colectomy and ileorectal 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.