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Finasteride May Become Prostate Cancer Preventive

Cheryl Thompson

A drug that inhibits the conversion of testosterone to a more potent form of the hormone may not only shrink an enlarged prostate but also prevent the development of cancer, researchers reported in an article released online Tuesday by the editors of the New England Journal of Medicine.

Among the nearly 19,000 men age 55 or older who participated in the federally supported Prostate Cancer Prevention Trial, those who received finasteride 5 mg/day for seven years had a 25 percent lower risk than placebo recipients of being diagnosed with prostate cancer. None of the men had signs or symptoms of prostate cancer when initially assigned to the finasteride or placebo group.

The study was originally scheduled to end in May 2004, but the independent data and safety monitoring committee recommended early termination because the primary objective had been met: the trial had determined whether seven years of finasteride therapy could reduce the prevalence of prostate cancer in older men. Also, so many men had enrolled in the study at its start and continued with their assigned treatment for the full seven years that the data from the remaining 14 percent of participants would not likely change the researchers' findings, the committee decided.

Finasteride treatment was not problem-free, however. Erectile dysfunction, loss of libido, reduced ejaculate volume, and abnormal breast enlargement occurred significantly more often in finasteride users than in placebo users. All of these adverse reactions are mentioned in the labeling for Proscar, the 5-mg finasteride product sold by Merck & Co. Inc. for the treatment of symptomatic benign prostatic hyperplasia in men with an enlarged prostate.

Merck provided the finasteride and placebo given to participants in the study. Participants underwent an annual digital rectal examination and measurement of prostate-specific antigen, a semiannual visit that included the recording of clinically important medical conditions and adverse events, and an every-three-month telephone interview regarding medical events that might have occurred since the previous visit.

Among the men in whom prostate cancer was detected during the study, those who received finasteride were significantly more likely than the placebo users to have a high-grade malignancy.

The researchers did not report how the men fared after their cancer diagnosis, although the person who oversaw the study for the National Cancer Institute, one of the funding agencies, said the finasteride recipients would be followed to determine whether their high-grade tumors actually manifest aggressive disease.

The researchers' article is scheduled for publication in the July 17 New England Journal of Medicine.