Finasteride prophylaxis appears to prevent or delay the onset of prostate cancer, however, finasteride may also accelerate the growth of high-grade cancers.
More than 18,000 men were randomized , age 55 or older to finasteride 5 mg/day or placebo. At baseline, digital rectal examination results were normal in all subjects, and prostate-specific antigen (PSA) levels were no more than 3.0 ng/mL. Among the 4368 men in the finasteride group treated for 7 years, prostate cancer was detected in 18.4%, compared with 24.4% of the 4692 assigned to placebo group, a significant difference (p < 0.001). Tumors of Gleason grade 7, 8, 9, or 10 occurred in 37.0% of the graded tumors in the finasteride group and 22.2% of those in the placebo group (p = 0.005). Five men in each group died from prostate cancer.
Treatment was temporarily discontinued by 18.3% of subjects administered finasteride and 9.8% of those given placebo because of side effects. Finasteride was more likely to affect sexual functioning, whereas placebo was more likely to be associated with genitourinary effects.
For a man considering using this medication, the greater absolute reduction in the risk of prostate cancer must be weighed against the smaller absolute increase in the risk of high-grade disease,say doctors.
Researchers, suggests that "finasteride may have created an environment in which high-grade cancers that were less dependent on androgens for their growth had a competitive advantage."
According to doctors , "Finasteride does not seem to be an attractive agent for the chemoprevention of prostate cancer." However, they do not advocate discontinuation of the drug when used to treat urinary symptoms, so long as patients undergo careful monitoring.