Finasteride and Prostate Cancer Risk

Bottom line: Finasteride at 5 mg reduced the overall incidence of prostate cancer by 25% in the PCPT trial. However, the trial also found a slightly higher rate of high-grade (Gleason ≥7) cancers in the finasteride arm, a finding many researchers attribute to detection bias rather than true causation. Men taking finasteride for AGA (1 mg) are at a lower systemic dose; the PCPT used 5 mg.

PCPT Trial Key Numbers

Outcome	Finasteride 5 mg	Placebo
Overall prostate cancer prevalence	18.4%	24.4% (25% relative reduction)
High-grade cancer (Gleason ≥7)	6.4%	5.1%
Absolute difference in high-grade cancers	1.3 percentage points

The Detection Bias Hypothesis

Finasteride reduces prostate volume by approximately 25%. A smaller prostate means biopsy needles sample a higher proportion of prostate tissue, making detection of small, clinically insignificant high-grade cancers more likely in the finasteride arm. Long-term follow-up (Thompson et al., 2013) found similar overall survival between arms and no significant difference in survival after a prostate cancer diagnosis. The FDA label includes a cancer warning but notes the clinical significance of the high-grade finding is uncertain.

Guideline Position

• Proscar label (FDA): Finasteride is not approved for the prevention of prostate cancer
• FDA: Added a label warning noting the PCPT high-grade cancer finding; does not conclude causation

Sources

• Thompson IM, et al. “The influence of finasteride on the development of prostate cancer.” N Engl J Med. 2003;349(3):215-224.
• Thompson IM, et al. “Long-term survival of participants in the Prostate Cancer Prevention Trial.” N Engl J Med. 2013;369(7):603-610.

See: PCPT trial full review | Long-term safety overview | Finasteride for BPH | Finasteride in prostate cancer context