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Finasteride Reduced Prevalence of Prostate Cancer, But Not Without Risks

Daily finasteride therapy reduced the prevalence of prostate cancer, but in men who did develop the disease, those taking finasteride - compared with placebo - were more likely to be diagnosed with high-grade disease.

Data from The Prostate Cancer Prevention Trial also indicates that sexual side effects were more common in men taking finasteride while more men using placebo reported urinary problems.

Ian M. Thompson, M.D., of the University of Texas Health Science Center in San Antonio, United States and colleagues randomised 18,882 men to receive daily finasteride (5 mg) or placebo for 7 years. The men were 55 years or older, had a prostate-specific antigen (PSA) level of 3.0 ng per millilitre or lower, and a normal digital rectal examination.

The men had annual digital rectal examinations and PSA measurements and were contacted every 3 months to record clinically significant medical conditions and side effects or interim medical events.

Final analysis in 4368 men taking finasteride and 4692 men taking placebo reveals that prostate cancer was detected in 18.4% of the finasteride and 24.4% of the placebo group. In those who developed prostate cancer, 6.4% of the men taking finasteride, compared with 5.1% of those on placebo, had tumours with Gleason scores of 7, 8, 9, or 10.

The finasteride group more commonly reported a loss of libido, reduced volume of ejaculate, erectile dysfunction, and gynecomastia while the placebo group reported more urinary urgency and/or frequency, prostatitis, urinary tract infection, and urinary retention.

While 7 years of finasteride treatment reduced the prevalence of prostate cancer in this study population by 24.8% the investigators stress that this reduction was achieved, "in a clinical trial marked by frequent monitoring for disease and was associated with an increased risk of diagnosis of high-grade prostate cancer."

In a related editorial, Peter T. Scardino, M.D. writes that this approach, "is destined to lead to the overdetection of histologically identified cancers of little clinical significance." Dr. Scardino of Memorial Sloan-Kettering Cancer Center in New York City adds that the high rate of detection of cancer in both study groups, "raises serious concern about the clinical significance of the cancers that were detected and the reduction achieved with finasteride."

The study results further suggest the possibility that finasteride therapy may accelerate the growth of high-grade cancers. This possibility coupled with the effects finasteride had on sexual function lessens the drug's attractiveness as a preventive agent, Dr. Scardino concludes.
N Engl J Med 2003;349:213-22.

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