CHICAGO—Dutasteride lowers the risk of prostate cancer by 23% in men with an increased risk of the malignancy, new findings show.

The findings come from the four-year Reduction by Dutasteride of Prostate Cancer Events trial, which randomly assigned 8,108 men aged 50-75 years to receive a daily 0.5-mg dose of dutasteride—a dual 5α-reductase inhibitor—or placebo.

Subjects had elevated PSA levels (2.5-10 ng/mL) and, within six months prior to study enrollment, biopsies showing no evidence of cancer. Investigators performed 10-core biopsies on the men at two and four years and “for-cause” biopsies when indicated.

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After two years, the researchers, led by Gerald Andriole, MD, Professor of Urologic Surgery at Washington University School of Medicine in St. Louis, diagnosed prostate cancer in 13.4% of dutasteride-treated men compared with 17.2% of placebo recipients. At four years, researchers diagnosed additional prostate cancers in 9.1% of dutasteride patients compared with 11.8% of placebo recipients.

Among those diagnosed with prostate cancer, dutasteride-treated men did not have an increased risk of aggressive tumors. Aggressive high-grade tumors (Gleason score 7-10) were found in 6.7% and 6.8% of the dutasteride and placebo groups, respectively. Researchers presented findings here at the American Urological Association annual meeting.

“We are very encouraged by this finding,” Dr. Andriole said. “Clearly, the data show dutasteride did not lead to more high-grade tumors. If the high-grade tumors in the dutasteride-treated men were similar in size to those in the placebo group, they would have been easier to detect due to the smaller size of the dutasteride-treated prostates. Dutasteride must be shrinking these tumors or at least preventing their growth.”

Previously, in the Prostate Cancer Prevention Trial, men who took finasteride, another 5α-reductase inhibitor, for seven years had a 25% reduced risk of prostate cancer. An initial analysis suggested that prostate cancers which developed in finasteride-treated men were more likely to be aggressive, but a subsequent analysis showed that this is not the case.