Finasteride Doesn't Cause Aggressive Forms Of Prostate Cancer

Whether to treat men at risk of prostate cancer with the drug finasteride has been the dilemma with doctors for the last six years. On one hand, the drug had been shown to prevent cancer in about one of every four patients who received it. On the other, those who did develop cancer while on the drug were 25 percent more likely to have a more aggressive form of the disease.

Now new research from Stanford University School ofMedicine appears to show that the drug did not cause those more aggressive forms of prostate cancer but simply made them easier to diagnose. The findings, which are to be published July 7 in Clinical CancerResearch, suggest that doctors can be less cautious in use of finasteride. 

The questions about finasteride treatment can be traced to 2003 when researchers published results from the Prostate Cancer Prevention Trial, a 7-year study that tracked 18,882 healthy men over age 55. That study assigned some of the participants to take finasteride and some to take a placebo. Finasteride, which reduces levels of the male hormonedihydrotestosterone and shrinks the prostate, was found to decrease the prevalence of prostate cancer by about 25 percent. But the drug also seemed to increase the chances that if a cancer was found, it would be fast-growing and likely to spread, again by about 25 percent. As a result, doctors rarely prescribe the drug as a preventive measure.

In reviewing this study, however, a number of researchers, including Stanford’s Joseph Presti Jr., MD, noticed that the initial analysis failed to detect a subtlety in the data: The increase in fast-spreading “high-grade” cancers wasn’t consistent across all groups and occurred disproportionately in those men who had developed warning signs of the disease.

In men who went through the study without developing any cancer warning signs, finasteride use made no difference in the rate of high-grade cancers diagnosed upon an exit biopsy. But the results were quite different for men who were biopsied after an abnormal digital rectal exam or because of a test showing elevated levels of prostate-specific antigen, a protein also known as PSA that can be unusually high in prostate cancer. Of those men, the ones on finasteride had an 11.5 percent rate of high-grade cancer, compared with 7.7 percent in the placebo group.

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