Radiation therapy for prostate cancer nearly doubles the risk of rectal cancer

Men who undergo radiation for prostate cancer have nearly double the risk of developing rectal cancer when compared to men who opt to have surgery to treat prostate cancer, according to a study published today in the American Gastroenterological Association (AGA) journal Gastroenterology. Men who receive radiation for prostate cancer have a 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.

“Men who have had prostate radiation should be aggressively monitored for rectal cancer starting five years after treatment,” said Nancy Baxter, MD, PhD, lead study author with the University of Minnesota Cancer Center. “This is the first time rectal cancer risk associated with prostate radiation has been quantified, and these findings may also have implications for patients treated with radiation for other pelvic cancers.”

Prostate cancer is the most commonly diagnosed malignancy in the United States. Although there is a high rate of survival associated with prostate cancer, a large number of men are left at risk for long-term consequences of their cancer treatment, including the development of other cancers.

Researchers at the University of Minnesota Cancer Center used data from the 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.

“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.

Since the study results are based on men who were treated for prostate cancer prior to 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 might still receive a high dose of radiation. Therefore, the risk of rectal cancer may still be substantial and thus, until proven otherwise, men treated with radiation for prostate cancer need monitoring for rectal cancer beginning five years after treatment.

Guidelines of multiple agencies and professional societies underscore the importance of colorectal cancer screening for all individuals 50 years of age and older. Approved tests include barium enema, FOBT, flexible sigmoidoscopy and colonoscopy. However, flexible sigmoidoscopy and colonoscopy are the best methods for accurately detecting rectal cancer. Each screening option has advantages and disadvantages. Patients undergoing radiation therapy for prostate cancer are advised to ask their doctor about one of the approved screening methods, regardless of their age.