The Prostate Cancer Prevention Trial (PCPT), a large randomized placebo-controlled trial of finasteride (an inhibitor of alpha-reductase), was performed in 18,882 men aged 55 years or older. At 7 years, the incidence of prostate cancer was 18.4% in the finasteride group versus 24.4% in the placebo group, a relative risk reduction (RRR) of 24.8% (95% confidence interval [CI], 18.6%–30.6%; P < .001). The finasteride group had more patients with Gleason grade 7 to 10, but the clinical significance of Gleason scoring is uncertain in conditions of androgen deprivation. High-grade cancers were noted in 6.4% of finasteride patients, compared with 5.1% of men receiving a placebo. The increase in high-grade tumors was seen within 1 year of finasteride exposure and did not increase during this time period.
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Finasteride decreases the risk of prostate cancer but may also alter the detection of disease through effects on prostate-specific antigen (PSA), prostate digital rectal examination, and decreased prostate volume (24%), creating a detection bias. Adjustment of PSA in men taking finasteride preserves the performance characteristics for cancer detection.
It is possible that finasteride induced the development of high-grade epithelial neoplasia, but this has not been demonstrated. With a finasteride-induced development of high-grade prostate cancer, a gradual and progressive increase in the number of high-grade tumors would have been expected for more than 7 years, compared with placebo; however, this was not the case. The increase in high-grade tumors was seen within 1 year of finasteride exposure and did not increase during this time period. An analysis of the PCPT data adjusted for the sources of detection bias found that finasteride reduced the incidence of Gleason 5 to 7 and Gleason 3 to 4 prostate cancer, but not Gleason 2 to 3 or Gleason 8 to 10. The reduction in the incidence of Gleason 7 (22%) was less than the reduction in the incidence of Gleason 5 (58%) and Gleason 6 (52%). An analysis using different methodologies found an overall reduction of both low-grade (Gleason <6) and high-grade (Gleason >7) cancers.