Men who took the


(MRK) - Get Merck & Co., Inc. (MRK) Report

drug finasteride, which affects male hormone levels, reduced their chances of getting prostate cancer by 25%, according to findings of a large study released Tuesday.

But not all of the study's findings are positive. Men in the study who developed prostate cancer while taking finasteride were more likely to have serious, high-grade forms of the disease. Furthermore, the incidence rate of prostate cancer in the trial, including those men taking a placebo, was far higher than expected.

Mixed Results

This good news-bad news is sure to spark a debate over whether doctors should start prescribing finasteride to men as a preventive treatment against prostate cancer. Data from the so-called Prostate Cancer Prevention Trial -- including the conclusion that finasteride may help prevent prostate cancer -- were published Tuesday in the online edition of

The New England Journal of Medicine

. But an accompanying editorial in the


concludes that "disturbing findings" in the study outweigh the positives, and that doctors should not be prescribing the drug to lower the risk of prostate cancer.

Merck currently sells finasteride under two brand names. As Proscar, the drug is used as a treatment for an enlarged prostate gland, a common ailment of aging men. A lower dose of the drug, sold as Propecia, is approved as a hair-loss treatment. Finasteride works by inhibiting an enzyme that converts testosterone into the more potent dihydrotestosterone, the primary male hormone in the prostate.

Combined, finasteride sales totaled about $550 million last year. Naturally, finasteride sales could soar if doctors began prescribing the drug to a significant number of men as a way to lower prostate cancer risk.

Merck shares were down 45 cents, or 0.7%, at $61.66 in Tuesday morning trading.

Prostate cancer is the most common cancer in men after skin cancer, and will affect nearly 221,000 men in the U.S. this year. About 29,000 men will die of the disease, according to the National Cancer Institute.

The Prostate Cancer Prevention Trial, funded by the NCI, enrolled nearly 19,000 men nationwide, who were randomized to take either 5 mg of finasteride or a placebo daily for seven years. Men enrolling in the study had no evidence of prostate cancer prior to entry. The study was scheduled to end in May 2004, but was stopped in March 2003, because the strong data collected to that point were not apt to change if the study continued to its conclusion, the NCI said.

When the study was closed, prostate cancer had been found in about 18% of the men who took finasteride, or 803 men out of 4,368. About 24% of men who took placebo, or 1,147 men out of 4,692, also had been diagnosed with prostate cancer. This works out to a statistically significant 24.8% reduction in the prevalence over the seven-year period. Many of the men with cancer had normal physical exams and clean clinical lab tests, but the cancer was found only because the trial required an end-of-study biopsy.

In addition, there was an abnormally high rate of detection of prostate cancer in this study. When the study was started, researchers expected to see cancer rates in the placebo group of around 6% -- instead, the final results came in at 24%.

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This puzzled even the authors of the study, who question whether cancer was overdiagnosed in the study, especially because the men enrolled in the study were not supposed to be at any higher risk for developing prostate cancer.

The final analysis was conducted on 9,060 men, subtracting those subjects who didn't complete seven years of treatment or those who didn't follow the study protocol, including agreeing to an end-of-study biopsy.

"Finasteride is the first drug found to reduce the risk of prostate cancer," said Dr. Ian Thompson of the University of Texas Health Sciences Center, who led the study. "The drug worked for men at low risk for prostate cancer, as well as those at high risk."

But while men taking finasteride seem to have a lower risk of developing prostate cancer, they were at greater risk for more serious forms of the disease. Overall, 6.4% of men on finasteride (280 men out of 4,368) had high-grade tumors. For men on placebo, 5.1% (237 men out of 4,692) had high-grade cancers, according to the findings.

The reasons for this are unknown and are still being studied. Finasteride affects the appearance of prostate cancer cells, which may lead to a false estimate of tumor grade when examined by a doctor. But finasteride may also cause more aggressive tumors to develop either by preventing low-grade tumors from forming, or by actually making the prostate gland more favorable to aggressive tumors, the study's researchers said.

"Millions of men may benefit from finasteride's ability to reduce prostate cancer risk," said Dr. Leslie Ford, M.D., associate director for clinical research in NCI's Division of Cancer Prevention, who oversaw the study. "As with any medical procedure or intervention, a decision to take finasteride is an individual one in which the benefits and risks must be considered."

But on a more skeptical note, Dr. Peter Scardino, author of the accompanying


editorial, writes, "Should finasteride now be recommended to men in order to lower their risk of prostate cancer? Several disturbing findings in the report argue that it should not."

Scardino, a urologist at Memorial Sloan-Kettering Cancer Center in New York, adds, "In the placebo group, cancer was detected four times as often as was expected -- in 24.4% rather than 6% of the men. Furthermore, the relative rate of high-grade cancers and the absolute number of such cancers were greater in the finasteride group than in the placebo group. How can we explain these findings?"

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