Drug Promises to Prevent Prostate Cancer

By LAURAN NEERGAARD : AP Medical Writer
Jun 25, 2003 : 12:53 am ET

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.

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 very 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 dummy pill.

The study of 18,000 older men, originally scheduled to run for another year, was abruptly stopped this month, and the New England Journal of Medicine rushed the results onto its Web site Tuesday.

"This trial proves prostate cancer, at least in part, is preventable," said Dr. Peter Greenwald, NCI's cancer prevention chief, who participated in the study himself and so far is cancer-free. "It's a huge step forward."

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. Some hormonal treatments can make prostate cancer cells initially appear more aggressive than they are. Researchers are tracking how those men fare.

--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.

"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, added Dr. Herman Kattlove of the American Cancer Society, who predicted a huge debate about its usefulness.

"If it were free of side effects, it would be another story," he said, citing impotence and loss of libido that were more common among Proscar users. "If it's not going to save your life, and it's just going to ruin your sex life, I won't."

How effective is Proscar? Track 1,000 men starting at age 63, and 60 will get prostate cancer by age 70. Eighteen of those cancers will be high-grade. Give those 1,000 men Proscar every day, and only 45 would get prostate cancer -- but 22 of them would be high-grade, the NCI estimated.

Proscar's other effects: Sexual problems were 5 percent to 13 percent more common among Proscar users. However, Proscar users had slightly fewer of the urinary problems that often accompany aging.

"There are very few prevention strategies that are not trade-offs," said Thompson, urging men to weigh their individual cancer risk and side-effect tolerance.

Proscar aside, the massive study could shed much-needed new light on other problems with prostate cancer. Today, there's no good way to predict who needs aggressive therapy and who has a slow-growing, unthreatening tumor. Scientists will use blood, biopsy and even some DNA samples given by study participants in hopes of solving that dilemma.