Baxter NN et al. (2005) Increased risk of rectal cancer after prostate radiation: a population-based study. Gastroenterology 128: 819–824

Radiation therapy for prostate cancer has been linked to an elevated risk of bladder cancer and other pelvic malignancies. A recent study by Baxter et al. now reveals that the risk of rectal cancer is similarly increased.

Using Surveillance, Epidemiology, and End Results registry data, a retrospective analysis was carried out on 85,815 men diagnosed with prostate cancer between 1973 and 1994. By comparing the incidence of rectal cancer in men who underwent radiation treatment (n = 30,552) and those who underwent surgery only (n = 55,263), an independent association was found between radiation treatment and development of rectal cancer. After adjusting for other factors, this corresponded to a 1.7-fold increase in risk in the radiation-therapy group, compared with the surgery-only patients. No significant associations were found between radiation therapy and the development of tumors at potentially irradiated sites (rectosigmoid, sigmoid and cecum) or in the remainder of the colon; thus, the observed increase in the risk of cancer was related to highly irradiated tissue only.

While these findings are unlikely to affect prostate cancer treatment patterns, the authors point out that there are implications for colorectal cancer screening. They recommend that screening for rectal cancer should start 5 years after prostate cancer radiation therapy.