The study looked at use of androgen deprivation therapy, a common type of treatment for prostate cancer that involves blocking the male hormone testosterone through either surgical removal of the testicles or a series of injections. It's been shown to benefit men with advanced cancers, but its benefit for less-advanced disease is unclear. Still, more than half a million men in the United States currently receive this therapy.

Researchers looked at data from 107,859 men aged 67 and older with prostate cancer, identified through the Surveillance, Epidemiology and End Results and Medicare linked database, which provides information about older adults with newly diagnosed cancer. Results of the study were published online in the Journal of the National Cancer Institute.

The study is the first to link androgen deprivation therapy for prostate cancer to an increased risk of colorectal cancer. The researchers found that the risk increased the longer a man received androgen deprivation therapy. Patients who had their testicles removed, a procedure called orchiectomy, had the highest rates of colorectal cancer.

Overall, the risk of colorectal cancer was still low -- less than 1 percent per year even among orchiectomy patients. But any increased risk should be carefully considered when using androgen deprivation therapy in cases when its benefit is not clear, the researchers say.

"Androgen deprivation therapy still continues to be used in situations where there are not evidence-based studies showing its benefit. When androgen deprivation therapy is clearly known to be beneficial, people should not shy away from using it. But where there's not solid evidence, this is potentially another harm," says lead study author Vahakn B. Shahinian, M.D., M.S., assistant professor of internal medicine at the University of Michigan Medical School and a member of the U-M Comprehensive Cancer Center.

Shahinian stresses that androgen deprivation therapy can be lifesaving for certain men with prostate cancer, and those patients should not hesitate to use it. The study authors suggest that continued routine preventive care, including colorectal cancer screening, is important during prostate cancer treatment.

Funding was provided by the National Cancer Institute, Sassella Stiftung Zurich, and Union Bank of Switzerland.

Prostate cancer statistics: 217,730 Americans will be diagnosed with prostate cancer this year and 32,050 will die from the disease, according to the American Cancer Society.

Note: If no author is given, the source is cited instead.

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