Men who receive radiation therapy for prostate cancer more likely to develop rectal cancer

Among men treated for prostate cancer, those who received radiation therapy were more likely to develop bladder or rectal cancer, according to a new study from the University of Michigan Comprehensive Cancer Center.

"Overall the incidence of these cancers is low. But when men have received radiation treatments, it's important to evaluate carefully any symptoms that could be a sign of bladder or rectal cancer," says senior study author Kathleen A. Cooney, M.D., professor of hematology/oncology and urology at the U-M Medical School.

The study, which will be presented at the American Society of Clinical Oncology annual meeting, looked at 441,504 men diagnosed with prostate cancer between 1992 and 2010. Men were identified from the Surveillance, Epidemiology and End Results (SEER) program, a network of National Cancer Institute-sponsored, population-based cancer registries that collect information on cancer diagnoses and treatment. SEER performs regular follow-up for survival and to capture new invasive cancer diagnoses.

The researchers looked at the number of secondary cancers that developed 10 or more years after men were diagnosed with prostate cancer. As a whole, men diagnosed with prostate cancer were at a lower risk of developing a second cancer. But when researchers looked at patients who received external beam radiation therapy, they found these patients were estimated to be 70 percent more likely to be diagnosed with a rectal cancer and 40 percent more likely for bladder cancer than the general public.

Radiation therapy is a standard treatment for prostate cancer and the researchers stress that their findings should not prohibit anyone from choosing this treatment, in particular men who are not good candidates for surgery.

"Prostate cancer has an excellent prognosis. But because patients typically survive a long time, it raises concerns about the risk of second cancers," says study author Elizabeth J. Davis, M.D., a fellow at the U-M Medical School. "Long-term survivors who have undergone treatment with radiation and their physicians should be careful to monitor for symptoms of bladder and rectal cancer."