Colon and anorectal cancer after pelvic irradiation.

Seventy-six cases of colon or anorectal cancer after pelvic irradiation for other malignant or benign lesions were reviewed. The patients were 13 men and 63 women with a mean age of 65 years; 67 percent had received irradiation for gynecologic malignancy. The cancer developed at a mean of 15.2 years after irradiation (peak frequency between five and ten years); 85 percent of the patients had a mild to prominent radiation reaction around the cancer. Of the 72 adenocarcinomas, 26 percent were mucinous. Only 17 percent of patients presented with symptoms of radiation proctitis, and the mean radiation dosages were not high. High radiation dosage and severe radiation damage may not be essential for radiation-associated colorectal cancer. The overall five-year survival rate was 48 percent. Close surveillance of the colon and anorectal regions of these high-risk patients at five years after irradiation is indicated.