A study from a group of researchers at the University of Illinois in Chicago suggests testosterone replacement therapy (TRT) such as implants and injections, can increase the risk of developing prostate cancer, which is known to affect 1 out of 7 men and is the second leading cause of cancer-related death.

While a number of risk factors are known such as older age, African-American ethnicity, family history, diet, and obesity, the link between testosterone and prostate cancer is still not established. While testosterone is a weak complete carcinogen, it is a strong tumor promoter in rats.

One of the authors of the study, Maarten C. Bosland, Ph.D., explained that in one experiment, the team noted prostate tumor growth in male rats receiving testosterone. One group had slow-release implants, another had standard testosterone implants. Both groups were then given a single dose of a carcinogen called N-nitroso-N-methylurea (MNU). Ten to eighteen percent of the rats with slow-dose testosterone implants developed prostate tumors, while an alarming 50 to 71 percent of those that had the standard implants developed tumors as well.

This suggests that extra doses of testosterone that did not affect serum levels, can still drive tumor growth. These findings, which are published in the journal Endocrinology, prompted Bosland and his team to conduct a safety and efficacy study of TRT for use in conditions other than hypogonadism. He explains the TRT industry makes over $2 billion worth of annual sales, but there is little research on the safety of these supplements. The only way to be certain is to conduct studies on humans.

Just recently, the FDA voted to mandate better labelling on TRT products as there has been a noted increase in male users who do not even have hypogonadism. They have also begun requiring TRT manufacturers to study the products’ effects on cardiovascular health.

“The potential of testosterone treatment to increase risk of prostate cancer, an androgen dependent malignancy, has been raised repeatedly. … Conclusive data on its safety for the prostate are lacking, probably in part because large scale testosterone therapy is a recent phenomenon and prostate cancer is a notoriously slow developing disease.” Maarten C. Bosland said in a MedPage Today interview.

Bosland points out that several studies have proven androgen inhibitors to be effective against these testosterone-fueled prostate tumors. These findings should already prompt researchers to look into the potentially cancer-causing effect of TRTs, and invest in long-term investigations.