Androgen deprivation therapy (ADT) is a widely-prescribed treatment in men with prostate cancer (PC), 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 (CRC). To determine whether prostate cancer patients taking androgen deprivation therapy are at an increased risk of colon cancer, an observational study of men with prostate cancer identified through the Surveillance, Epidemiology, and End Results (SEER) database of the National Cancer Institute was undertaken. 107’859 men aged 67 years or older who were diagnosed with prostate cancer between 1993 and 2002, with follow-up through 2004 were identified. 46% of these men received ADT in the form of gonadotropin-releasing hormone (GnRH) agonists and 5% in form of orchiectomy. After adjustment for confounding variables such as age, socio-economic status, comorbidites including diabetes and obesity and for tumor characteristics there was an increase of the relative risk of up to 37% to develop colorectal cancer among the men treated with ADT compared with those who were not with the highest risk in patients with orchiectomy. Furthermore, the longer the men took ADT, the greater their risk of developing colorectal cancer. Gillessen