Prostate cancers detected during 5α-reductase inhibitor use are smaller, de-differentiated, but confined when compared to controls.

Rationale: To compare cancers detected during use of 5α-reductase inhibitors (5αRI) with cancers detected in untreated controls stratified for tumor size.

Methods: Prostate biopsies were performed on 235 consecutive patients "for cause" (elevated or rising PSA, positive digital rectal examination, or focal hypoechoic lesion). Fifty patients were excluded for a prior diagnosis of cancer, leaving 185 as the study group (5αRI=41, control=144).