New Data Show Drug's Benefits in Preventing Prostate Cancer

Stephanie Doyle

May 22, 2008

May 22, 2008 (Orlando, Florida) — A reanalysis of data from the Prostate Cancer Prevention Trial (PCPT), which was initially reported in 2003, has confirmed the study's main finding — that regular use of the 5-alpha-reductase inhibitor finasteride reduces the risk for prostate cancer — and seems to have laid to rest the fear that patients taking the drug have an increased risk for high-grade disease.

The new findings, which show that after adjustment for prostate volume, finasteride reduces the risk for most prostate cancers, were presented here at the American Urological Association (AUA) 2008 Annual Meeting.

"In a country where more than 200,000 men face this diagnosis each year, finasteride would have substantial public-health consequences," Ian M. Thompson Jr, MD, chair of the department of urology at the University of Texas Health Science Center at San Antonio, told Medscape Urology.

Dr. Thompson, principal investigator for the Southwest Oncology Group in the original PCPT study, said the PCPT, which involved more than 18,000 men 55 years of age and older, was discontinued early in June 2003 because researchers noted that although finasteride reduced prostate cancer by up to 25%, men taking the drug appeared to have more aggressive prostate tumors if and when they did develop the disease. Because of this, some experts worried that finasteride was triggering higher-grade cancers.

The new analysis, led by researchers from New York-Presbyterian Hospital/ Weill Cornell Medical Center, could allay those fears.

Because of its ability to shrink the prostate, finasteride has long been used by physicians to treat benign enlarged prostate, so when researchers accounted for the reduction in prostate volume, the disparity in tumor aggressiveness between the finasteride and placebo groups disappeared.

Physicians use the Gleason scale to grade the aggressiveness of prostate tumors on the basis of tumor characteristics (the scale ranges from 2 to 10, with 10 indicating the most highly aggressive cancers). After their initial analysis, PCPT investigators discovered that men taking finasteride had fewer prostate cancers overall, but a higher incidence of grades 7, 8, 9, and 10 cancers.

This was alarming, because higher-grade potentially metastatic prostate cancers are the real cause for clinical concern. Investigators needed to determine whether the finding was real or whether it was some kind of methodologic affect.

The research team theorized that because finasteride shrinks the prostate, doctors were better able to spot highly aggressive tumors in patients taking the drug.

Researchers reviewed the PCPT data on biopsies taken from the 18,882 men in the study. They adjusted for treatment type, age, race, family history of prostate cancer, baseline prostate-specific antigen (PSA) levels, and each patient's prostate volume.

They found a significant reduction in the incidence of prostate cancers, even the higher-grade cancers, in men taking finasteride, compared with placebo. Most important, finasteride was associated with significant declines in tumors with Gleason scores of 5, 6, and 7, which comprise 72% of all prostate cancers. For tumors with Gleason scores of 8, 9, and 10, after adjustment for prostate volume, the incidence for men taking finasteride was no higher than for men not taking the drug.

Although it is too early to say that the drug prevents the disease, it might help suppress it when it occurs, the researchers said.

In the meantime, researchers need to keep prostate volume in mind when conducting trials that assess the anticancer properties of prostate-shrinking medications.

Not everyone at the AUA meeting agreed with the new study results, but Brantley Thrasher, MD, chairman of the department of urology at the University of Kansas, in Lawrence, said the initial troubling questions related to the PCPT appear to have been answered.

"They were paramount in people's minds,'' said Dr. Thrasher, who was not involved with the study. "I think they have done a very good job at answering those questions. There are compelling data here."

Dr. Thrasher said the question now is who to treat with finasteride.

"There are some remaining questions that loom large," he said. "Do we tell everyone to take it? Only African American men? Men with a family history? All low-risk men? Should we give everyone this drug? I don't know the answers."

Dr. Thompson said that "any man over 55 who is having his PSA checked on an annual basis can have his risk reduced by taking finasteride. I am a baby boomer. I have a 1 in 6 chance of being diagnosed with prostate cancer. I turn 55 next year. And about this time next year I will say: 'Write me a prescription for finasteride'."

The PCPT trial was funded by the US National Cancer Institute and Merck, the maker of finasteride. The authors have disclosed no relevant financial relationships.

American Urological Association 2008 Annual Meeting: Abstract 470. Presented May 18, 2008.


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