A common treatment for prostate cancer puts men at increased risk for diabetes and cardiovascular disease, according to a new study.

"Men with prostate cancer have high five-year survival rates, but they also have higher rates of non-cancer mortality than healthy men," says study author Nancy Keating, M.D., M.P.H., of Harvard Medical School. "This study shows that a common hormonal treatment for prostate cancer may put men at significant risk for other serious diseases. Patients and physicians need to be aware of the elevated risk as they make treatment decisions."

The principal therapy for prostate cancer involves blocking the body's production of the hormone testosterone. This is done either by removal of the testes or, more commonly, by regular injections of a type of drug called a gonadotropin-releasing hormone (GnRH) agonist.

However, little is known about the efficacy of these drugs in treating men with less-advanced local or regional prostate cancer, many of whom receive this therapy. Earlier studies have found GnRH agonists to be associated with obesity and insulin resistance, a precursor to diabetes.

"Our study found that men with local or regional prostate cancer receiving a GnRH agonist had a 44 percent higher risk of developing diabetes and a 16 percent higher risk of developing coronary heart disease than men who were not receiving hormone therapy," says Keating, who is also a physician at Brigham and Women's Hospital.

"Doctors should think twice about prescribing GnRH agonists in situations for which studies have not demonstrated improved survival until we better understand the risks of treatment," says co-author Matthew Smith, M.D., Ph.D., associate professor of medicine at HMS and a medical oncologist at Massachusetts General Hospital.

The study appears in the Sept. 20 2006 Journal of Clinical Oncology.