updated 4/27/2009 4:06:36 PM ET 2009-04-27T20:06:36

A drug already sold for other prostate problems significantly cut the chances of prostate cancer being found in men with an increased risk of the disease, doctors reported Monday.

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In a large international study, dutasteride, sold as Avodart, lowered the chances of a prostate cancer diagnosis by 23 percent after four years of use.

Tens of thousands of men each year face a problem like those in the study: worrisome results from prostate cancer screening tests and biopsies that come back negative.

There's no question that many had small tumors that were not detected, yet the drug still lowered the risk of cancer being found years later, said Dr. Gerald Andriole of Washington University School of Medicine in St. Louis.

He led the study in the United States and reported results Monday at an American Urological Association conference in Chicago. The study was sponsored by Avodart's maker, British-based GlaxoSmithKline PLC, and Andriole has consulted for the company.

Dutasteride now joins finasteride, sold as Merck & Co. Inc.'s Proscar and in generic form, as a potential prostate cancer prevention drug. In February, health experts recommended that men consider these medicines if they are regularly getting screened for the disease. Prostate cancer

Both shrink the prostate and curb testosterone, a hormone that helps cancer grow, but dutasteride does this in two ways and more completely than finasteride. An earlier study found that finasteride lowered the risk of prostate cancer being found in men with no known increased risk of the disease.

The new study involved 8,200 men ages 50 to 75 with high PSA blood test scores but no sign of cancer on biopsy. They were given dutasteride or dummy pills and new biopsies two and four years later.

After two years, prostate cancer was found in 17 percent of men on dummy pills and 13 percent of those on the drug. After four years, it was found in another 12 percent of men on the placebo and 9 percent on dutasteride.

Rates of aggressive tumors were the same — about 7 percent in each group. That was a relief, because finasteride at first seemed to raise this risk. More study suggests that isn't the case — it's just that these tumors are easier to find in men taking the drug because it reduces prostate size.

Not all experts are convinced. These drugs shrink less aggressive tumors more than they do the most serious kind, and may be masking the problem, said Dr. William Catalona, a Northwestern University prostate cancer expert who invented the PSA blood test.

"If you give any hormone therapy, it will temporarily make things look good. I don't think we're preventing prostate cancer here," just delaying its eventual detection, Catalona said.

More time is needed to tell, said Dr. Otis Brawley, the American Cancer Society's chief medical officer and one of the scientists overseeing the dutasteride study.

"The only way you can figure out whether you have an aggressive tumor or not is to follow the guys and see what ultimately happens" in their death rates, Brawley said.

Some men experienced side effects from dutasteride, including trouble having an erection.

How many men will opt to take that drug or finasteride is unclear. The drugs cost about $3 a pill. To prevent a single additional case of cancer, 71 men would have to take finasteride for seven years, doctors previously calculated. A similar estimate for dutasteride is not available yet, Andriole said.

The advice in February that men consider these drugs has sparked more interest from the public, including one man who had two brothers with prostate cancer, said Dr. Lee Ponsky, prostate cancer chief at University Hospitals Case Medical Center in Cleveland. Doctors started the man on finasteride.

At Fox Chase Cancer Center in Philadelphia, "more doctors are talking about it with patients," said surgeon Dr. Robert Uzzo.

Prostate cancer is the most common non-skin cancer in American men. An estimated 186,000 new cases and 28,660 deaths from it occurred last year.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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