The influence of finasteride on the development of prostate cancer

Original Internist,  Sept, 2003  

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Background: Androgens are involved in the development of prostate cancer. Finasteride, an inhibitor of 5a-reductase, inhibits the conversion of testosterone to dihydrotestosterone, the primary androgen in the prostate, and may reduce the risk of prostate cancer.

Methods: In the Prostate Prevention Trial, we randomly assigned 18,882 men 55 years of age or older with a normal digital rectal examination and a prostate-specific antigen (PSA) level of 3.0 ng per milliliter or lower to treatment with finasteride (5 mg per day) or placebo for seven years. Prostate biopsy was recommended if the annual PSA level, adjusted for the effect of finasteride, exceeded 4.0 ng per milliliter or if the digital rectal examination was abnormal. It was anticipated that 60% of participants would have prostate cancer diagnosed during the study or would undergo biopsy at the end of the study. The primary end point was the prevalence of prostate cancer during the seven years of the study.

Results: Prostate cancer was detected in 803 of the 4,368 men in the finasteride group who had data for the final analysis (18.4%) and 1,147 of the 4,692 men in the placebo group who had such data (24.4%), for a 24.8% reduction in prevalence over the seven-year period (95% CI, 18.6-30.6%: P<0.001). Tumors of Gleason grade 7, 8, 9, or 10 were more common in the finasteride group (280 of 757 tumors [37.0%], or 6.4% of the 4,368 men included in the final analysis) than in the placebo group (237 of 1,068 tumors [22%]: P<0.001 for the comparison between groups: or 5. 1% of the 4,692 men included in the final analysis; P=0.005 for comparison between the groups). Sexual side effects were more common in the finasteride-treated men, whereas urinary symptoms were more common in the men receiving the placebo.

Conclusions: Finasteride prevents or delays the appearance of prostate cancer, but this possible benefit and a reduced risk of urinary problems must be weighed against sexual side effects and the increased risk of high-grade prostate cancer.

Thompson IM, et al. N Engl J Med, July 17, 2003; 349 (3):215-224.

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