A treatment mainstay for prostate cancer puts men at increased risk for diabetes and cardiovascular disease, according to a large observational study published in the Sept. 20 Journal of Clinical Oncology.

“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, MD, MPH, assistant professor of health care policy and of medicine at 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 systemic therapy for prostate cancer involves blocking testosterone production. This is done either by removal of the testes (bilateral orchiectomy), or more commonly, by regular injections of a gonadotropin-releasing hormone (GnRH) agonist drug. GnRH agonists are the main therapy for metastatic prostate cancer and may also improve survival for some men with locally-advanced cancers.

However, little is known about the efficacy of GnRH agonists 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, MD, PhD, associate professor of medicine at HMS and a medical oncologist at Massachusetts General Hospital. “For men who do require this treatment, physicians may want to talk with their patients about strategies, such as exercise and weight loss, which may help to lower risk of diabetes and heart disease.”

Given the number of men receiving GnRH agonists, often for many months or years, these increased risks can have important implications for the health of prostate cancer survivors, says Keating. Additional studies are needed to fully understand the biological mechanisms responsible for these increased risks.

Prostate cancer is the most frequently diagnosed cancer among men, affecting more than 200,000 men in the United States every year. With prostate cancer’s favorable prognosis, however, decisions about treatments are particularly important because adverse effects and complications of treatments may impact overall health and quality of life more than prostate cancer itself.

The study assessed whether androgen deprivation therapy was associated with an increased incidence of diabetes, coronary heart disease, myocardial infarction, or sudden cardiac death by examining data from approximately 73,000 men age 66 or older who were diagnosed with local or regional prostate cancer.

This work was supported by the Prostate Cancer Specialized Program of Research Excellence (SPORE) of the National Cancer Institute, one of the National Institutes of Health.