The study found that men who receive radiation for prostate cancer have about 70 percent higher risk of developing rectal cancer than those who underwent surgery, a risk similar to that posed by having a family history of the disease.

Nancy Baxter, M.D., Ph.D., colon and rectal surgeon at the University of Minnesota's Medical School and Cancer Center, led the research. "While the findings of our study do not suggest that prostate cancer treatment should change, we recommend that the potential for developing rectal cancer be included in conversations between doctors and patients when considering the individualized course of treatment and surveillance for patients with prostate cancer," said Baxter.

"Additionally, we recommend that men who have had prostate radiation should be monitored for rectal cancer starting five years after treatment," Baxter added.

The scientists used data from the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Registry to evaluate the effect of radiation on development of cancer in the rectum. More than 85,000 men, age 18 to 80, were included in this retrospective, population-based study.

Radiation therapy for prostate cancer has been associated with an increased rate of pelvic malignancies, particularly bladder cancer. Findings of this study suggest that direct radiation to the rectum increases the risk of developing rectal cancer, but does not affect the risk of cancer in other parts of the colon.

Since the study results are based on men who were treated for prostate cancer before 1995, the risk of developing cancer may be reduced by the evolution of radiation delivery techniques. However, researchers say that even with today's technology, some portions of the rectum still receive a high dose of radiation.; Source: University of Minnesota