In 2003, finasteride became the first drug to prevent prostate cancer in a large, prospective study, the Prostate Cancer Prevention Trial (PCPT) ¹. Finasteride reduced the overall occurrence of prostate cancer by 25 percent, but concerns were raised because men taking the drug had a slightly higher number of high-grade prostate cancers, which tend to be aggressive. Two studies ² in the September 19 Journal of the National Cancer Institute provide reassurance that the drug was probably not causing the high-grade cancers. Rather, finasteride may have simply made it easier to detect high-grade cancers. Dr. M. Scott Lucia of the University of Colorado Health Sciences Center, who coauthored the PCPT results and led one of the new studies, discusses the findings.

What did you learn from your study?
The data we collected best support the hypothesis that the use of finasteride enhances the detection of high-grade prostate cancers at biopsy. Finasteride decreased overall prostate volume by 27 percent in men diagnosed with high-grade cancer. We compared the results of prostatectomies and biopsies for 489 men. Of the men who had high-grade tumors at prostatectomy, biopsy correctly identified the cancer as high-grade 70 percent of the time in the finasteride group but only 50 percent of the time in the placebo group. This effect was likely a result of the decrease in prostate volume combined with a selective inhibition of low-grade cancer. Although we cannot rule out the possibility that finasteride might influence the growth of some high-grade prostate cancers, the results suggest that the impact of finasteride on high-grade cancer is less than originally thought, or perhaps even that it has no effect.

Have the new findings changed your view of the PCPT results?
One has to interpret the results of the original study with the knowledge that there is a bias in detecting high-grade cancers. We now know that finasteride interferes with two important measures that we use to detect prostate cancer - the prostate-specific antigen test and digital rectal exam - by making these tests more sensitive for cancer. This bias makes it very difficult to interpret the results. But finasteride is clearly a better drug than it initially appeared to be. We were also reassured to find that the high-grade cancers in the finasteride group appeared to be less extensive on biopsy than in the placebo group.

Are the results good news for men?
Yes. The PCPT results were important because we showed for the first time that you can prevent prostate cancer by taking an agent, in this case finasteride. Up until this point the concept of prostate cancer chemoprevention had been largely theoretical, but we have shown this can happen. The new results bring more good news because the risks of taking finasteride, which were a deal-breaker for many men back in 2003, are probably not as great as originally thought, though the precise risks are not known. Finally, many men take finasteride for benign prostatic hyperplasia (enlargement of the prostate), and the results are reassuring that the drug is safe for use in that setting. This may be the most important piece of good news for men.