Men taking androgen deprivation therapy (ADT) for prostate cancer may have an increased risk of colorectal cancer, according to a study published online November 10 in The Journal of the National Cancer Institute.

Androgen deprivation therapy is a widely-prescribed treatment in men with prostate cancer, although its usage for low-risk disease remains controversial, given the adverse side effects, including osteoporosis, cardiovascular disease, diabetes and obesity; the last two are risk factors for colorectal cancer.

To determine whether prostate cancer patients taking androgen deprivation therapy are at an increased risk of colon cancer, Dr Silke Gillessen, of the Cantonal Hospital in St. Gallen, Switzerland, and colleagues, did an observational study of men with prostate cancer identified through the Surveillance, Epidemiology, and End Results (SEER) database of the National Cancer Institute. Specifically, they identified 107,859 men aged 67 years or older who were diagnosed with prostate cancer between 1993 and 2002, with follow-up through 2004. The men received the ADT either in the form of gonadotropin-releasing hormone (GnRH) agonists, or an orchiectomy.

The researchers found that after adjustment for confounding variables such as age and socio-economic status, there was a 30-40% relative increase in the rate of colorectal cancer among the men treated with ADT compared with those who were not. Furthermore, the longer the men took ADT, the greater their risk of developing colorectal cancer. However, further study would be needed to determine the risk with treatment over longer periods than could be observed in this study.

The authors write that the study results could have "important implications" for men with prostate cancer taking ADT, especially those with localised, slow-growing disease, for whom the duration of ADT is generally longer.

In an accompanying editorial, Dr Jennifer H. Lin and Dr Edward Giovannucci, of Brigham and Women's Hospital in Boston write that the study shows that an elevated risk of colorectal cancer may be an additional consideration in the decision to use ADT, especially given the side effects and their effect on quality of life.

Source: The Journal of the National Cancer Institute