The drug Proscar (search) helps prevent prostate cancer and could lengthen the lives of many men, researchers say.

This is true even though the drug appears to increase the likelihood that some men will get more advanced prostate cancer (search), they say.

Prostate cancer is the most common type of cancer for U.S. men after skin cancer, says the American Cancer Society. The ACS estimates that one in six men will develop prostate cancer. However, many fewer men -- one in 33 -- will die of prostate cancer, and prostate cancer death rates are dropping, says the ACS.

Lifesaving Effects

Prostate cancer grows in response to the male hormone testosterone. Proscar inhibits testosterone. It has already been approved by the FDA to treat men with enlarged prostates. It's also sold under the name Propecia to treat male pattern baldness.

The drug entered the spotlight in the recent Prostate Cancer Prevention Trial, where it cut prostate cancer prevalence by nearly 25 percent. The trial's results were so strong that the study of almost 19,000 men was stopped a year early.

But the news wasn't all rosy. The testosterone-lowering drug was linked to a greater incidence of advanced prostate cancer. Of men diagnosed with prostate cancer, nearly 12 percent of those taking Proscar had advanced prostate cancer, compared with 5 percent who took a placebo.

Was Proscar worth it for men to take on a large scale? Yes, says the new study, which appears in the April 1 edition of the journal Cancer.

The researchers crunched the numbers from the Prostate Cancer Prevention Trial, applying them to all men aged 55 or older from 1993 to 1997. They calculated Proscar's lifesaving potential.

If every man in the U.S. age 55 or older took Proscar, more than 316,000 person-years would be saved in a decade, the researchers estimate. For example, more than 316,000 men would live a year longer than without the drug.

Even if advanced cancers increased by about 7 percent, Proscar would still allow more than 262,000 men to live a year longer, write Joseph Unger, MS, and colleagues. Unger works at the Fred Hutchinson Cancer Research Center in Seattle.

Proscar's potential shouldn't be overlooked out of fear, the study suggests. The researchers point out again that prostate cancer would be prevented in 25 percent of men that take Proscar.

By Miranda Hitti, reviewed by Michael W. Smith, MD

SOURCES: Unger, J. Cancer, April 1, 2005; vol 103. WebMD Medical News: "Drug Prevents Prostate Cancer." WebMD Medical News: "Q&A: Drug for Prostate Cancer Prevention." American Cancer Society, "How Many Men Get Prostate Cancer." News release, John Wiley & Sons Inc.