A large, retrospective population study suggests that prostate cancer treatments that lower male sex hormones may increase the risk of colorectal cancer. Men treated with gonadotropin-releasing hormone (GnRH) agonists or surgical removal of their testicles (orchiectomy) to lower their testosterone and PSA levels experienced an increased risk of colorectal cancer of about 20 to 40 percent. The findings were reported online November 10 in the Journal of the National Cancer Institute.

More than half of nearly 108,000 prostate cancer patients identified in the linked SEER-Medicare database received androgen deprivation therapy between 1993 and 2002. Approximately 90 percent of those men had been treated with GnRH agonists, and the rest had had orchiectomy. They were followed for about 5 years after their prostate cancer diagnosis.

After adjusting for possible confounders such as obesity, diabetes, and radiotherapy, the researchers found a dose-response effect for GnRH agonists in which colorectal cancer risk increased with longer duration of treatment. Compared with prostate cancer patients who received no hormone treatments, those who had GnRH agonist therapy for 13 to 25 months had a 19 percent increase in colorectal cancer risk, those who had GnRH agonist therapy for longer than 25 months had a 31 percent increase in risk, and those who had orchiectomy had a 37 percent increase in risk.

Lead author Dr. Silke Gillessen of Kantonsspital St. Gallen in Switzerland and her colleagues noted that an inverse association between androgen levels and colorectal cancer risk is biologically plausible. “Androgen receptors are present in both normal and malignant human colonic tissues, and in various animal studies, administration of androgens protects against colon carcinogenesis, whereas androgen ablation promotes it,” they wrote. The authors went on to say that their evidence “may have broader implications beyond the field of prostate cancer” because nearly half a million men in the United States develop androgen deficiency each year.

source: NCI