A controversial drug that can prevent prostate cancer appears to be even more beneficial than previously thought.
Two studies to be published in the Journal of the National Cancer Institute found the drug finasteride not only shrinks enlarged prostate glands and reduces the risk of prostate cancer but also improves detection of the most lethal tumors.
Finasteride is one of only a handful of drugs that have been shown to prevent cancer. (Tamoxifen, which cuts breast cancer risk in half, is another.) But doctors have been reluctant to prescribe finasteride because it was believed to promote the growth of high-grade, or aggressive, tumors.
A 2003 study published in the New England Journal of Medicine showed that men who took finasteride had an 18.4 percent chance of being diagnosed with prostate cancer over a seven-year period, compared with 24.4 percent for men who took a dummy pill -- a 25 percent reduction. But the incidence of high-grade tumors was higher in the finasteride group: 6.4 percent vs. 5.1 percent.
From that trial, it was not clear whether finasteride caused the extra cases of aggressive cancer or merely created a situation in which more high-grade cancers were detected.
On Tuesday, researchers said new evidence strongly suggests that finasteride, also known by the trade name Proscar, makes it easier to detect high-grade tumors early, when they are potentially more treatable.
In one study, Dr. Peter Gann of the University of Illinois at Chicago and colleagues found the drug increases the likelihood of finding high-grade cancer cells in a prostate biopsy by decreasing the volume of prostate tissue.
Reanalysis of data from the 2003 study showed detection of high-grade cancers in the placebo group increased as the size of the prostate decreased. They also found the average prostate in the finasteride group was 25 percent smaller. When they statistically controlled the analysis for prostate size, the difference between the prevalence of high-grade tumors in the two groups disappeared.
A second study, by the Southwest Oncology Group, reached the same conclusion. "By shrinking the prostate gland, finasteride makes a biopsy more sensitive," said senior author Dr. Ian Thompson.
The studies were released online Tuesday, ahead of their publication in the journal next week.
Gann said the studies don't mean all men should take finasteride to prevent prostate cancer, but they "should provide reassurance to men who have used it in the past or are using it currently" to shrink enlarged prostates -- the use for which the drug was approved in 1992.
Thompson, however, said men should be told routinely about the potential benefits of finasteride when they come to the doctor's office for prostate screening, just as those who are at risk of heart disease are told about the benefits of statin drugs.
The Southwest Oncology Group is a large, federally funded clinical-trials network based at the University of Michigan. The same group conducted the 2003 study, known as the Prostate Cancer Prevention Trial.
Proscar was developed to treat the benign prostate enlargement that often comes with aging. A lower dose of finasteride is approved as Propecia to treat male-pattern baldness. The drug works by preventing testosterone from converting to another hormone that fuels prostate enlargement and cancer growth.
The drug is generally well tolerated, but in the 2003 trial, slightly more men taking finasteride reported sexual side effects (erectile dysfunction or loss of libido) than those taking the placebo.
Judy Peres writes for the Chicago Tribune.
PROSTATE CANCER FACTS
The drug finasteride has been shown to reduce the risk of getting prostate cancer by 25 percent, but there is no evidence it can reduce deaths from the disease.
The average U.S. male's risk of getting prostate cancer: 1 in 6
Estimated U.S. cases in 2007: 218,890
Estimated deaths: 27,050