Q&A

Does finasteride prevent prostate cancer?

J Fam Pract. 2003 November;52(11):828-848
By
Alphaeus M. Wise, MD
James J. Stevermer, MD, MSPH
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  • BACKGROUND: Androgens play an important role in the development of prostate cancer. Finasteride blocks 5-reductase, an enzyme that converts testos-terone to the more potent dihydrotestosterone, and may therefore help prevent prostate cancer.
  • POPULATION STUDIED: The researchers recruited 24,482 men into the study over 3 years from 221 outpatient centers. Of these, 18,882 were randomized into finasteride or placebo. The men that were included in the study were aged 55 years or older, with no significant coexisting conditions, normal digital rectal exams, and a prostate-specific antigen (PSA) level <3.0 ng/mL. The majority of men not randomized (71%) were not enrolled due to an elevated PSA level.
  • STUDY DESIGN AND VALIDITY: This was a randomized, double-blind, placebo-controlled trial. We are not told how patients were recruited or whether allocation was appropriately concealed. Enrolled patients were placed on a placebo for 3 months, with PSA levels drawn before and after that 3-month period. If their adherence to placebo use was within 20% of expected and their PSA remained <3.0 ng/mL, the men were randomized to receive either finasteride 5 mg or a placebo daily.
  • OUTCOMES MEASURED: The primary outcome of this study was the prevalence of prostate cancer. The presence of prostate cancer was based on biopsy at the end of the study, if it had not been previously diagnosed during biopsy or transurethral resection of the prostate. Other outcomes included mortality, percent of high-grade cancers (Gleason score 7–10), and biopsy rates. The researchers also gathered data on sexual and urinary side effects.
  • RESULTS: The number of men in the final analysis was 9060 (48% of enrollees). The incidence of prostate cancer was lower in the finasteride group (18.4% vs. 24.4%; P=.001; number needed to treat=16). These rates were much higher than the 6% and 4.5% the researchers expected. Significantly more high-grade cancers (Gleason grade 7–10) were seen in the finasteride group (6.4% vs 5.1%; P=.005; number needed to harm=77). Researchers found no significant difference in mortality between the 2 groups (7.0% vs 6.7%). Only 5 men in each group (0.05%) died of prostate cancer.
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PRACTICE RECOMMENDATIONS

Treatment with finasteride will, over 7 years, decrease the prevalence of prostate cancer but increase the likelihood of developing a high-grade cancer. For every 1000 men given finasteride for prostate cancer, 62 will not develop prostate cancer. In addition, 35 men will not develop benign prostatic hypertrophy, 27 will have less urinary urgency or frequency, and 21 will report less urinary retention.

However, of those that develop prostate cancer, 13 will have higher-grade cancer (Gleason score 7 or higher), 59 will have erec-tile dysfunction, 58 will have a loss of libido, and 131 will have reduced volume of ejaculate. This study provides no information on the clinical significance of reducing the overall rate of cancer, while increasing higher-grade tumors. Since it is unclear whether finasteride reduces morbidity or mortality, it cannot be recommended for the routine prevention of prostate cancer.

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