A steroid inhibitor that shrinks the prostate gland--and in low doses treats baldness--also helps prevent prostate cancer, researchers have found. The results come from a massive, 7-year trial of nearly 19,000 men. But although the drug, called finasteride, caused a 25% reduction in prostate cancer, it also boosted the risk of aggressive prostate cancer among those diagnosed with the disease. Physicians now hope to figure out who's most likely to benefit from the drug.
When finasteride was approved in 1992, it was intended to treat men with an enlarged prostate. (Its hair-restoring properties were noted later.) Physicians also wondered whether its ability to block the natural conversion of testosterone to a more powerful male hormone, called dihydrotestosterone, in the prostate could prevent cancer. Previous research had linked male hormones to the onset of prostate cancer. Some scientists worried that vast numbers of men might begin taking finasteride as a preventive, before it had been proven to do the job. So they speedily--many at the time said too speedily--launched the Prostate Cancer Prevention Trial, recruiting 18,882 healthy men over age 55 and randomly dividing them into two groups. One received finasteride, and the other got a placebo.
After 7 years, the researchers, led by Ian Thompson of the University of Texas Health Science Center in San Antonio, were left with 9060 men. In the finasteride group, 18%, or 804 men, had developed prostate cancer. In the placebo group the number was 24%, or 1147 men. (The typical incidence is about 6%; the team believes it found more because biopsies were routinely performed at the end of the study.) The difference was so striking that Thompson and his colleagues halted the study a year ahead of schedule.
The drug had side effects, however, including some problems with sexual arousal. Of greater concern were the higher rates of prostate cancer classified as aggressive: It developed in 6.4% of the men in the finasteride group, compared with 5.1% in the placebo group.
The difference in more serious prostate cancer rates, although small, "looks like a real phenomenon," says Peter Scardino, head of urology at Memorial Sloan-Kettering Cancer Center in New York City. He notes that the increase could be misleading; it's possible, for example, that the drug changes the architecture of cancer cells in the prostate, making them only look worse. Either way, says Scardino, the study needs to be followed up with others that evaluate the drug's effect in, say, men at higher risk of prostate cancer.