Nearly 4 percent of American men in their 60s are thought to be on testosterone replacement therapy.
This was the main conclusion of a study that analyzed nationwide registry data on over a quarter of a million - mostly white - men residing in Sweden.
The research, led by New York University (NYU) Langone Medical Center, New York, NY, features at the American Urological Association annual meeting in San Diego, CA, May 6-10, 2016.
In fact, the researchers found not only that men prescribed testosterone replacement therapy (TRT) for longer than a year showed no overall increase in risk of developing prostate cancer, but that if anything, their risk for aggressive disease was 50 percent lower than equivalent men not prescribed TRT.
The motive for the study was to try and settle a debate about the link between TRT and prostate cancer risk, say the researchers.
They note that experts suggest an aging "boomer" generation, and heavy marketing by the drug industry has fueled a rapid rise in use of TRT in the last 10 years, despite little being known about the long-term risks of the therapy.
They say surveys show TRT use has more than tripled since 2001, and now over 2 percent of American men their 40s and nearly 4 percent of those in their 60s are thought to be on TRT.
Once men reach their 30s, they can expect their testosterone levels to drop naturally by around 1 percent per year.
However, while a recent pooled analysis finds no increase in prostate cancer risk in men on TRT, it was found to have several limitations, such as the studies included in the review were small, did not look at long-term TRT use, or lacked a control group.
Only long-term TRT tied to 50 percent lower risk
For their study, the NYU-led researchers chose to look at a very large sample from Sweden. The country is ideal for this type of study because it has comprehensive, nationwide registries of medical data on prostate cancer and prescription drugs.
They found 38,570 men who developed prostate cancer during 2009-2012, and among whom 284 were prescribed TRT before their cancer was diagnosed.
The researchers compared data on these men with data on another 192,838 age-matched controls who did not develop prostate cancer; this group included 1,378 men who had been prescribed TRT.
An initial analysis showed men on TRT had a 35 percent higher risk of being diagnosed with prostate cancer shortly after starting their treatment, but the researchers say the increase was only in cancers with a low risk of spreading and were likely diagnosed because of more doctor visits and biopsies performed early on.
They note that the 50 percent lower risk of being diagnosed with aggressive prostate cancer was seen only in men who had been prescribed TRT for over a year. They found no difference in risk between gels and other ways of delivering TRT (such as by mouth, injection, or patch).
Lead investigator Stacy Loeb, assistant professor of urology and population health at NYU, and a specialist in prostate cancer, says much of the concern about the link between TRT and cancer risk is that one of the ways that prostate cancer is treated is with drugs that dramatically reduce rather than raise male sex hormones.
But," she notes, "when used appropriately by men with age-related low testosterone who are otherwise healthy, testosterone replacement has been shown to improve sexual function and mood."
Prof. Loeb explains that their findings suggest men should keep their testosterone levels steady and within a normal range and perhaps those who find their levels drop below 350 nanograms per deciliter and who experience symptoms should talk to their doctor about whether TRT would be right for them.
"Based on our findings, physicians should still be watching for prostate cancer risk factors - such as being over the age of 40, having African-American ancestry, or having a family history of the disease - in men taking testosterone therapy, but should not hesitate to prescribe it to appropriate patients for fear of increasing prostate cancer risk."
Prof. Stacy Loeb
The researchers plan to investigate why low testosterone might be a trigger for aggressive prostate cancer, and why holding it within the normal range might protect against the disease.