Findings from a new government study may ease worries about the safety of a commonly used hormone-blocking drug that can lower a man's chances of developing prostate cancer.
The drug is sold as Proscar by Merck & Co. and in generic form as finasteride to treat urinary problems from enlarged prostates. It may be more commonly known in its lower dose form, Propecia, which is prescribed to treat hair loss.
The drug cut prostate cancer risk by 30 percent without raising the risk of dying of an aggressive form of the disease as earlier results hinted it might.
The research could prompt a fresh look at using the drug for cancer prevention. Experts say it could prevent tens of thousands of cases each year, saving many men from treatments with seriously unpleasant side effects.
The new study was published in The New England Journal of Medicine on Aug. 15.
Finasteride's link to prostate cancer risk dates back to a previous 2003 study also in the New England Journal of Medicine that found the drug curbed men's risk of developing prostate cancer - also by 30 percent. But, there was a small increase in risk of aggressive tumors among its users. Some researchers said that by shrinking the prostate, the drug was just making these tumors easier to find in a biopsy sample -- not causing them.
But the concern led the Food and Drug Administration (FDA) to turn down the drug for cancer prevention and warnings were added to its label.
Now, with 18 years of follow-up data from that previous study, researchers are reporting that men on the drug were no more likely to die than those not taking it.
That's reassuring because if the drug were truly spurring lethal tumors, there would have been more deaths among its users as time went on, said Dr. Michael LeFevre, a family physician at the University of Missouri.
LeFevre wrote an editorial that appears with the new research.
He is one of the leaders of the U.S. Preventive Services Task Force, an independent panel of doctors who advise the federal government on treatment and screening guidelines. The group has not taken a stance on finasteride for prevention but has, saying the blood test may do more harm than good from catching slow-growing cancers that may never pose a serious health threat.
What presents more risk, the panel said in 2012, was serious side effects from biopsies or surgeries following a positive PSA test, including erectile dysfunction, incontinence and other sexual and urinary problems.
Although about 240,000 new prostate cancers are diagnosed each year in the United States, only about 30,000 prove fatal.
The latest researcher, led by Dr. Ian Thompson, an oncologist at the Cancer Therapy and Research Center in San Antonio who also led the 2003 research, was done to see whether finasteride could lower the risk of prostate cancer in men who were getting screened with annual PSA blood tests, as many still opt to do.
Researchers randomly assigned nearly 19,000 men aged 55 or older with no sign of prostate cancer on blood tests to take finasteride or placebo pills for seven years. When the study ended, those who had not been diagnosed with prostate cancer were offered biopsies to check for hidden signs of the disease.
For the latest analysis, researchers tracked the study participants for a longer time -- 18 years in all since enrollment began. Only about 10 percent of men on finasteride developed prostate cancer versus 15 percent of those on dummy pills. Aggressive tumors were found in 3.5 percent of men on the drug versus 3 percent of the others, but the numbers were not statistically significant. Yet 78 percent of both groups were alive after 15 years.
That means the drug cannot be recommended to prolong life, just to ease suffering by preventing disease, LeFevre said.
"You may be preventing cancers that don't need to be prevented" because so few are life-threatening, but screening is finding these tumors anyway and leading to unnecessary treatments, he said. Reducing that number is a valid reason to use a prevention drug, he said.
Not all experts agree that's enough of a reason.
"Taking the pill won't prevent death from cancer, but it gets rid of the cancers that aren't going to cause a problem," CBS News contributor Dr. David Agus, an oncologist who leads Westside Cancer Center at the University of Southern California who was not involved in the research, said Thursday on CBS This Morning.
"So why take this?" he asked. "We need to change medicine so we can not treat these cancers that aren't going to cause a problem."
Finasteride's other impact is financial. Proscar and a similar drug, GlaxoSmithKline PLC's Avodart, cost about $4 a pill. Generic finasteride is available for less. Insurers cover it when prescribed to treat urinary problems but may not pay if it's used solely for cancer prevention.
Study author Thompson told USA Today that the FDA is unlikely to update finasteride's label based on his new study. He said the drug's price today is too low to inspire a company to spend the time and money necessary to petition the FDA.
The drug can cause hot flashes, fatigue, weakness, low sex drive and trouble having sex.over sexual side effects including decreased libido and reported cases of male infertility and poor semen quality that improved after patients stopped taking the drugs.
"A man certainly needs to know what he's getting into if he decides to take this," said LeFevre.