Benefits from Finasteride Chemoprevention
Harms from Finasteride Chemoprevention
Benefits and Harms of Other Prevention Interventions

Note: Separate PDQ summaries on Prostate Cancer Screening, Prostate Cancer Treatment, and Levels of Evidence for Cancer Screening and Prevention Studies are also available.

Based on solid evidence, chemoprevention with finasteride reduces the incidence of prostate cancer, but the evidence is inadequate to determine whether chemoprevention with finasteride reduces mortality from prostate cancer.

Description of the Evidence

• Study Design: Evidence obtained from randomized controlled trials.
• Internal Validity: Good for the outcome of incidence, poor for the outcome of mortality.
• Consistency: Not applicable.
• Direction and Magnitude of Effect: Absolute reduction in incidence over 7 years was 6% (24.4% with placebo and 18.4% with finasteride); relative risk reduction for incidence was 24.8% (95% confidence interval [CI], 18.6%–30.6%). There was no difference in the number of men dying from prostate cancer in the two groups, though the number of deaths was small.
• External Validity: Fair, because of small numbers of African American and Hispanic men.

Men in the finasteride group had statistically significantly more erectile dysfunction, loss of libido, and gynecomastia than men in the placebo group. Men in the finasteride group had a statistically significant incidence of high-grade (Gleason sum 8–10) cancers during the study.[1] Whether this was a histological artifact or not is uncertain.

Description of the Evidence

• Study Design: Evidence obtained from randomized controlled trials.
• Internal Validity: A randomized controlled trial of finasteride for the prevention of prostate cancer used an interview (rather than a patient-completed questionnaire) to examine erectile dysfunction and libido during treatment (rather than both before and during treatment).
• Consistency: Good (evidence other than the randomized controlled trial supports these effects).
• Direction and Magnitude of Effect: Statistically significant increases in the following outcomes were observed in the finasteride group (an additional 9% of men in the finasteride group discontinued therapy at least temporarily because of one of these side effects):
  • Percentage in finasteride group versus percentage in placebo group:
    • Reduced volume of ejaculate (60.4% vs. 47.3%).
    • Erectile dysfunction (67.4% vs. 61.5%).
    • Loss of libido (65.4% vs. 59.6%).
    • Gynecomastia (4.5% vs. 2.8%).
• External Validity: Fair, because of small numbers of African American and Hispanic men.

There is inadequate evidence to determine whether the prevention strategies of dietary change (i.e., reducing dietary fat or increasing fruits and vegetables), or vitamin E (alpha-tocopherol), selenium, or lycopene supplementation, are effective in reducing prostate cancer incidence or mortality.

Description of the Evidence

• Study Design for Vitamin E and Selenium: Evidence obtained from randomized controlled trials, in this case secondary endpoints from randomized trials.
• Study Designs for the Other Interventions: Evidence obtained from cohort or case-control studies. Evidence obtained from ecologic and descriptive studies (e.g., international patterns studies, time series).
• Internal Validity: Fair.
• Consistency: Poor.
• Direction and Magnitude of Effect: Uncertain.
• External Validity: Fair.

References

1. Thompson IM, Goodman PJ, Tangen CM, et al.: The influence of finasteride on the development of prostate cancer. N Engl J Med 349 (3): 215-24, 2003.  [PUBMED Abstract]
   
   

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