Radiation-induced cancers of the colon and rectum: assessing the risk.

Individuals who have received pelvic irradiation are reported to be at increased risk to develop subsequent malignancies in the large bowel. In order to plan appropriate follow-up for these patients, it is necessary to understand the magnitude of their risk. In this paper we review the literature on colorectal cancer after irradiation and estimate the excess risk based upon available data. Women who are irradiated for gynecologic cancer may have a relative risk for subsequent colorectal cancer of 2.0-3.6 based on best estimates. This risk is calculated independent of any risk imposed by underlying disease. These women are appropriate targets for careful surveillance for colorectal cancer.