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WEDNESDAY, July 16, 2003 (HealthDayNews) -- A drug used to combat male baldness and shrink benign prostate glands also prevents prostate cancer, says a new government-sponsored study.
Men who took finasteride for seven years had a 25 percent lower chance of developing the disease during the trial, which was halted 15 months early because of the promising results.
"This trial proves that prostate cancer, at least in part, is preventable," says Dr. Peter Greenwald, director of the National Cancer Institute's Division of Cancer Prevention and Control who was also a participant in the trial. "It is a huge step forward for cancer research."
Results of the findings appear in the July 17 issue of the New England Journal of Medicine; they were first reported at a June 24 news conference.
Finasteride is the first drug shown to prevent prostate cancer, but a few potentially significant hitches exist, the researchers noted at the news conference. Although the men who took the medication had fewer prostate tumors, those tumors that did develop seemed slightly more likely to be especially aggressive. What's more, the drug was linked to an increase in such sexual side effects as impotence, a reaction that might deter some men from taking it.
Finally, the researchers say, there's no evidence yet that taking finasteride over time can reduce the death rate from prostate cancer.
That question "is impossible to answer at this time," says study co-author Dr. Leslie Ford, a researcher at the National Cancer Institute, which funded the trial.
Finasteride is sold as Proscar and Propecia by Merck & Co., which provided the drug used in the study. The medication does not have U.S. Food and Drug Administration approval for preventing prostate cancer, but Merck plans to ask the agency for an expedited decision on the issue.
Prostate cancer is the second most common cancer in men, affecting more than 220,000 in the United States each year. Of those, roughly 29,000 will die of the disease. Many of the rest may suffer a variety of troubling symptoms, ranging from sexual dysfunction to urinary incontinence.
The results of the study suggest that finasteride could prevent or delay 15 cases of prostate cancer in every 1,000 men who take the drug, Ford says. However, it might lead to an additional four cases of aggressive tumors in the men who develop the disease.
But Dr. M. Scott Lucia, another co-author of the study and a pathologist at the University of Colorado, says the link between finasteride and so-called "high-grade" tumors is fuzzy. Although the drug could be spurring the growth of these cancers, Lucia and his colleagues don't think that's happening.
Instead, Lucia says, finasteride may be altering the appearance of prostate cancer cells under a microscope so that they resemble aggressive tumors but don't act like them.
Finasteride blocks an enzyme that converts the male sex hormone testosterone into dihydrotestosterone, or DHT, a potent form of the molecule that's common in the prostate. Many prostate tumors are sensitive to DHT. Indeed, men with a genetic defect that keeps them from making the hormone don't get the disease, and a frequent treatment for the tumors is "chemical castration" to deprive the body of sex hormones.
The government study, known as the Prostate Cancer Prevention Trial, started with almost 18,900 men aged 55 and up with no signs or symptoms of prostate cancer. Half were given 5 milligrams a day of finasteride, and half took sugar pills.
At the end of the study, about 9,000 men remained; many of the others had dropped out, been excluded from finishing by the early end, refused a final tissue sample or died.
Among the men who didn't get finasteride, 24 percent developed prostate cancer, compared with 18 percent of those taking the drug -- a 25 percent difference. Of those tumors, 6.4 percent in the men on finasteride were considered aggressive upon biopsy, versus about 5 percent in the group that wasn't taking the drug.
Dr. Ian M. Thompson, a urologist at the University of Texas Health Science Center and leader of the research, says men and their doctors will need to assess the risks and benefits of taking finasteride to prevent prostate cancer.
Men with a strong family history of the disease and black men in particular, whose risk of dying from prostate cancer is nearly twice that of whites, may be inclined to embark on the therapy, he says. Similarly, men who are concerned about their risk of the disease for other reasons also may want to consider the drug.
The American Cancer Society issued a cautious statement about the findings.
"The study will no doubt prompt a lot of men to start asking their doctors whether they should be on the drug, and we would encourage men to carefully weigh their options as this information is very new," says Harmon Eyre, the group's chief medical officer. "There are still some important unanswered questions, especially regarding side effects, whether it can benefit men at increased risk, especially African-Americans, who are twice as likely as white men to die of prostate cancer, and the mechanism by which men taking the drug develop higher grade tumors."