Testosterone raises the risk of prostate cancer in an animal model, according to a University of Illinois at Chicago researcher, who urges caution in prescribing testosterone therapy to men for non-medical reasons.
The findings are published online, ahead of print, in the Endocrine Society's journal Endocrinology.
The study found that testosterone on its own is a weak carcinogen in male rats. When combined with the cancer-causing chemical N-nitroso-N-methylurea (MNU), testosterone significantly increases the frequency of prostate cancer.
Maarten Bosland, professor of pathology at the UIC College of Medicine, conducted two animal studies to see how testosterone dosage affected the incidence of prostate cancer.
Rats were given testosterone using one, two or four slow-release implant devices. Before being given testosterone, some rats received injections of the carcinogen MNU. The rats were compared to a control group that received MNU but not testosterone.
Ten to 18 per cent of animals that received testosterone but not the carcinogen developed prostate cancer. When the rats were exposed to both testosterone and the carcinogen, 50 to 71 per cent developed prostate cancer.
Even when the testosterone dose was too low to elevate the hormone's levels in the bloodstream, half of the rats developed prostate tumors. Animals that were exposed to the carcinogen but not testosterone did not develop prostate cancer.
''If these same findings hold true in humans, there is serious cause for public health concern,'' said Bosland, who notes that there are no current data to indicate testosterone heightens the risk of prostate cancer in humans.
Testosterone ''therapy'' has recently become popular among middle-aged and older men with low testosterone levels.
However, there is some evidence that it offers no health benefits, and the treatment may increase the risk of cardiovascular disease.
Caution should be used when prescribing testosterone for non-medical reasons until adequate human studies are available, Bosland said.
''Low testosterone levels in men should not be considered a disease that requires treatment,'' he said.
The research was supported in part by the Dutch Cancer Foundation and the National Institutes of Health grant.