Testosterone Linked to Prostate Cancer in Rats

FDA to Weigh Risks, Benefits of Testosterone Drugs
FDA to Weigh Risks, Benefits of Testosterone Drugs
In rats, testosterone appeared to raise the risk for prostate tumor growth.

Testosterone appeared to promote prostate tumor growth while simultaneously worsening the effect of exposure to carcinogens in rats, new data published in Endocrinology suggest.

Marten C. Bosland, DVSc, PhD, of the University of Illinois at Chicago, conducted two dose-response studies evaluating prostate cancer incidence in rats.

Injections of the carcinogenic chemical N-nitroso-N-methylurea (MNU) were administered to some rats before receiving testosterone via slow-release implant devices. These rats were then compared with a control group that received MNU but no testosterone.

Results showed that from 10% to 18% of rats receiving testosterone but no MNU developed prostate carcinomas. Testosterone was also linked to a significant increase in the number of rats with malignant tumors at any site when compared with controls, but the therapy on its own did not produce specific tumors at other sites, according to a press release.

Testosterone, however, appeared to boost the carcinogenic properties of MNU, with prostate cancer developing in 50% to 71% of rats exposed to both.

This finding held true even when the testosterone dose was too low to raise circulating levels of the hormone, with half the rats developing prostate tumors.

Rats exposed to MNU but no testosterone did not develop prostate cancer.

“This research demonstrates that testosterone on its own is a weak carcinogen in male rats,” Dr. Bosland said in the press release. “When it is combined with cancer-causing chemicals, testosterone creates a hospitable environment for tumors to develop. If these same findings hold true in humans, there is serious cause for public health concern.”

In light of the growing number of men initiating testosterone therapy, these study results, although very preliminary, could have important implications for clinical practice down the road.

 “Since the growth of testosterone therapy is relatively recent and prostate cancer is a slow-moving disease, there are at present no data to determine if testosterone could heighten the risk of prostate cancer in humans,” Dr. Bosland said.

“While human studies are conducted, it would be prudent to limit testosterone prescriptions to men with symptomatic clinical hypogonadism and avoid testosterone use by men for non-medical purposes, including addressing normal signs of aging.”


  1. Bosland MC. Endocrinology. 2014;doi:10.1210/en.2014-1688.