Drug may prevent prostate cancer, but not all men will want it

WASHINGTON -- Scientists have discovered that a drug that shrinks enlarged prostates and fights baldness also cuts men's chances of getting prostate cancer, the first success in a long quest to prevent the No. 2 cancer killer of men.

But not every man will want to use the drug, called finasteride: Sexual side effects aside, it may actually increase aggressive tumors in some.

Finasteride is sold under the brand name Proscar to treat the benign prostate enlargement so common with aging and, in a much lower dose, as Propecia to fight baldness.

"Finasteride may not be right for all men," cautioned Dr. Leslie Ford of the National Cancer Institute, which paid for the research. Men and their doctors should "take the time to review this data and make informed choices."

Prostate cancer strikes 220,000 U.S. men annually and kills almost 29,000; so even limited use of Proscar promises "extraordinary public health potential," said Dr. Ian Thompson of the University of Texas Health Sciences Center in San Antonio, who led the research.

Alters hormone level

Proscar alters levels of a male hormone, the testosterone relative DHT. Men with naturally low levels of DHT have less prostate cancer -- and black Americans, who have a high risk of prostate cancer, have high DHT levels.

Researchers tested whether reducing DHT could prevent cancer. The results: Men who took Proscar daily for seven years had 25 percent fewer prostate cancers than men given a placebo.

But some troubling findings have critics questioning just how often Proscar should be used:

Men who developed prostate cancer while taking Proscar were more likely to have tumors that appear to be aggressive, what doctors term "high grade." Some 6.4 percent of Proscar patients were diagnosed with high-grade tumors, compared with 5.1 percent of men given dummy pills.

No one knows if Proscar alters the prostate's hormone environment in a way that favors growth of more aggressive tumors or if that was a fluke.

Another quirk questions the true value of Proscar's benefit. Researchers diagnosed prostate cancer in four times more placebo patients than expected, partly because every study participant got a prostate biopsy even if blood tests for cancer-signaling PSA were normal. Those biopsies often found small, early-stage tumors -- and in the real world, wouldn't have been done.