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Study Links Low T Drugs to Prostate Cancer in Rats

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Weights, water bottle, syringe and measuring tape

Men who use popular testosterone replacement therapy to treat Low T (low testosterone) may increase their risk for prostate cancer, according to researchers who recently tested some of the drugs.

The study, led by professor Maarten Bosland of the University of Illinois at Chicago’s College of Medicine, found that rats that exposed to a carcinogen did not develop cancer but that 10 to 18 percent of ones that were exposed to testosterone did.

In addition, 50 to 71 percent of the rats exposed to both the carcinogen and testosterone developed prostate cancer – and usually more than one tumor.

“I was totally amazed about how strong testosterone can work to promote the formation of prostate cancer in these animals,” Bosland told Time.

The findings led researchers to believe that not only can testosterone cause cancer on its own, but it also can accelerate tumor growth in the presence of other carcinogens. Even low doses of the hormone replacement drug were enough to create tumors, according to the study.

They also led doctors to echo what other peers and other researchers already have said, that more testing is “urgently needed” because of the growing number of middle-age and older men drawn to Low T drugs.

Specifics of the Illinois Study

In the Illinois study, researchers observed three groups of rats. The first group was exposed to a carcinogen. The second group was exposed to testosterone drugs. And the third group received both the carcinogen and testosterone.

Researchers observed the rate of prostate tumor growth in all three groups. Rats in the testosterone groups received the hormone through implants, and the injected carcinogen was a toxic chemical called N-nitroso-N-methylurea (MNU).

Bosland and his team conducted two experiments, experiment A which lasted for 72 weeks and B which lasted for 95 weeks. In A, rats had  one or two testosterone implants and an injection of MNU, and in B, two to four implants with or without MNU.

MNU alone did not cause prostate cancer, but testosterone treatment alone induced prostate carcinomas in 10 to 18 percent of rats. The addition of MNU to long-term testosterone treatment caused cancer growth in all animals, even rats with only one testosterone implant.

Animals with two implants had the most dramatic rise in tumor growth and cancer incidence elevated 67 to 71 percent, according to the study. Four or five rats in experiment B had two to three tumors.

Prior to this study, about five studies using rats also showed a link between testosterone therapy and prostate cancer, Bosland said.

Testosterone Sales Boom

The rapid increase in the number of men taking testosterone to treat symptoms of Low T – such as fatigue and low libido – over recent years concerns many doctors who say the safety and effectiveness of these drugs is not known. Low T clinics are popping up in many cities and drug companies are riding the wave of men eager to regain lost youth.

Sales of drugs such as Eli Lilly’s Axiron, Pfizer’s Depo-Testosterone and AbbVie’s AndroGel – the top selling testosterone product – reached $2 billion and are primed to make even more. With sales like this, it’s more imperative to do proper human trials.

While rodents might not be able to determine what will happen in men, Bosland thinks the risk of prostate cancer may carry over.

“Absent of having solid human studies, we won’t be able to say that—it’s just an extra warning signal,” Bosland told Time. “But I think it’s a clear indication that there is risk.”

FDA Pushes for More Heart Studies, New Labels

The concerns over prostate cancer aren’t the only safety risks that may stem from testosterone drugs. Just last month the Food and Drug Administration (FDA) put together a panel of experts to examine the risks of heart attacks and strokes linked to the drugs. The panel concluded more tests for safety were needed.

The FDA panel also voted that labels on all of these products need to be clearer on what health conditions the drugs are intended to treat. Testosterone therapy is only approved to treat men with actual clinically diagnosed hypogonadism – a condition where the body fails to produce enough testosterone.

“Whether these symptoms are a clinical consequence of the age-related decline in endogenous testosterone has not been established, and therefore, the need to replace testosterone in these older men remains debatable,” the panel said in a statement.

Men File Lawsuits against Testosterone Manufacturers

A number of studies surfaced linking Low T drugs to an increased risk of heart attack and stroke. Shortly after, a number of men filed lawsuits against testosterone manufacturers after they suffered heart attacks, strokes and blood clots. The men claim they were not warned about the risk.

Patrick Miller of Hopatcong, N.J., filed one of the latest lawsuits. Miller, 54, took Eli Lilly’s Axiron in September 2012 and suffered a heart attack in October of the same year. His suit accuses Lilly of failing to warn patients about the risks and marketing it as safe and effective despite the risks.

“In essence, the defendant marketed and sold testosterone as a lifestyle drug meant to make men feel younger and increase libido,” according to Miller’s court filing.

Other companies are listed as defendants in multidistrict litigation, including: Endo Pharmaceuticals, Pfizer, AbbVie, Abbott Laboratories, Actavis and Auxillium Pharmaceuticals.

Until more studies are done, Bosland remains cautious.

“I would urge caution,” he told Med Page Today. “I would not take this treatment, and I would not recommend it to anyone else until adequate studies have been done.”

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