Drug promises to prevent prostate cancer -- but not everyone benefits

WASHINGTON (AP) -- Scientists have discovered the first drug that promises to prevent prostate cancer, but deciding who should use it won't be easy: Sexual side effects aside, it may actually increase aggressive tumors in some men.

The drug is finasteride, already sold as a treatment for enlarged prostates under the brand name Proscar.

Men who took Proscar daily for seven years cut their chances of getting prostate cancer by nearly 25 percent compared with men given a dummy pill, researchers report in the New England Journal of Medicine Tuesday.

The results were strong enough that the study of 18,000 men age 55 and older, originally scheduled to run for another year, was stopped this spring.

Proscar has "extraordinary public health potential ," said the study leader, Dr. Ian Thompson of the University of Texas Health Sciences Center in San Antonio. He said the drug could conceivably cut by a quarter the 220,000 U.S. men who will be diagnosed with prostate cancer.

Proscar worked equally well for men at low risk of prostate cancer, and those at high risk -- black men and those whose fathers and brothers had the disease.

Some troubling findings have critics questioning just how often Proscar should be used.

"It looks like Proscar prevented little tiny, insignificant cancers, but did nothing for high-grade cancers or maybe even allowed them to become more common," said Dr. Peter Scardino of New York's Memorial Sloan-Kettering Cancer Center, who wrote a cautionary editorial accompanying the research. "That doesn't sound like a very good trade-off to me."

The study didn't test whether taking Proscar helped men live longer.