Shrinking Impact

The prescription drug finasteride may be linked to a reduction in prostate cancer incidence.

by Alicia Di Rado

The prescription drug commonly used to shrink an enlarged prostate—and at a low dose, to prevent hair loss—also appears to prevent some cases of prostate cancer, according to a study that involved USC/Norris Comprehensive Cancer Center oncologists and patients.

The New England Journal of Medicine published the findings in its July 17, 2003 issue.

The Prostate Cancer Prevention Trial, funded by the National Cancer Institute (NCI) found that 25 percent fewer men taking the drug finasteride developed prostate cancer than men who were not taking the drug. The NCI halted the study in June 2003, nearly a year early, because conclusions were unlikely to change.

It is the first prevention study to show that a drug can impact risk for prostate cancer, the most common cancer in American men other than skin cancer. Nearly 221,000 American men were diagnosed with prostate cancer in 2003.

However, physicians are cautious about the results.

“I would want to see that the drug has actually improved survival,” says Eila C. Skinner, M.D., associate professor of clinical urology at the Keck School of Medicine of USC. “While this study does suggest finasteride may have an effect on the prostate, it may be too early to recommend that men take this drug.”

USC/Norris and Skinner are part of the Southwest Oncology Group, or SWOG, a group of cancer researchers at medical centers around the country. SWOG researchers coordinated the prevention trial, which began in October 1993 at 221 sites nationwide.

Nearly 19,000 men age 55 and older who had no evidence of prostate cancer enrolled in the trial during its first three years.

Some of the men took a daily finasteride pill, while others took a placebo. Physicians performed regular exams on participants and monitored them for prostate cancer, as well as side effects and other health problems.

Over seven years, about 18 percent of men in the finasteride group developed prostate cancer, compared to 24 percent of men in the placebo group.

Almost all the prostate cancers found in the participants, regardless of whether they were taking finasteride or a placebo, were found in an early stage.

However, digging deeper into the results raises questions.

First, prostate cancer was found among men taking a placebo at a rate four times greater than expected, which casts some doubt on whether the cancers were clinically relevant. Men taking a placebo had more low-grade cancers, which can ordinarily be caught early through screening and have a better chance for cure. They even may be occult cancers that grow so slowly that men who have them usually die of other causes before the cancer might pose a threat.

“If finasteride only lowers the incidence of low-grade cancers, it might not have any effect on survival,” Skinner says.

Results showed that men taking finasteride were more likely to develop high-grade cancers than the men taking a placebo. These cancers may be more aggressive and more likely to spread.

When used to treat a non-cancerous enlargement of the prostate, finasteride is known as Proscar. But many consumers may know it as Propecia, a significantly lower-dosage pill used to treat baldness.

Researchers do not know if the low-dose finasteride used for hair loss affects prostate cancer risk. They only tested finasteride at the higher dose found in Proscar. Skinner recommends that men wishing to reduce their prostate cancer risk talk with their physician.

Although they stopped the study, researchers will continue analyzing blood and tissue samples collected in the trial. They will look at the molecular biology of prostate cancer to better understand who is at risk for developing the cancer and if any particular men would benefit from taking finasteride.