The use of androgen-deprivation therapy (ADT) to treat prostate cancer is often reserved for recurrent disease or cases in which other treatments are contraindicated. It can also be used as an adjuvant to radiation therapy. It's estimated that hundreds of thousands of men use ADT, which reduces the levels of the male hormones that spur the growth of prostate cancer cells. However, ADT may also be linked to an increased risk of colon cancer, according to a recent observational study. As a result, the study's authors urge caution in prescribing the treatment, at least for early stage prostate cancer, because other studies haven't shown a clear benefit in doing so.

Gillessen and colleagues culled data from the Surveillance, Epidemiology, and End Results-Medicare database to identify 107,859 men 67 years old or older who were diagnosed with prostate cancer between 1993 and 2002. Of those men, 55,901 (51.8%) underwent androgen deprivation, either medically or surgically. Most (89%) received gonadotropin releasing hormone (GnRH) agonists; around 10% underwent orchiectomy.

After adjusting for variables that could have an impact on the risk of colon cancer, including a diagnosis of diabetes or obesity, the authors found a 30% to 40% relative increase in the rate of colon cancer among men who had received ADT, compared with those who didn't.

The absolute risk of colon cancer over five years, however, was much lower: 1.8% in men who didn't receive ADT, 2.2% in men who took GnRH agonists, and 3.2% in men who had an orchiectomy, wrote Vahakn B. Shahinian, one of the study's authors and an assistant professor of medicine at the University of Michigan, in an e-mail to AJN. The authors also found a dose-response effect related to the duration of ADT, with the risk of colon cancer increasing with continued therapy.

Frank delaRama, clinical nurse specialist in oncology and genomics at the Palo Alto Medical Foundation, said that nurses should help patients put the study's results into perspective. "It isn't a huge absolute risk and not anything that would cause a huge change in treatment," delaRama said.

Authors of an accompanying editorial wrote that the study's results underscore how important it is for patients with prostate cancer to get colonoscopies and follow a healthful lifestyle, which can help to "counter some of the drawbacks of antiandrogen therapies."-Linda Wilson