MRI Regression Does Not Exclude Pathological Progression During Active Surveillance in Men Receiving Dutasteride

<title>Abstract</title> <p> Objective To evaluate the biochemical, volumetric, radiologic, and pathological effects of dutasteride in men undergoing active surveillance (AS) for low-risk localized prostate cancer. Methods This multicenter observational cohort study included 101 men managed with AS, comprising 64 patients receiving dutasteride and 37 controls. Baseline and follow-up assessments (minimum 1 year) included prostate-specific antigen (PSA), prostate volume, PSA density, multiparametric magnetic resonance imaging (mpMRI), and repeat biopsy. MRI regression was defined as a reduction in PI-RADS score or lesion disappearance, whereas pathological progression was defined as ISUP grade upgrading and/or more than three positive biopsy cores. Results Compared with controls, the dutasteride group showed greater reductions in PSA, prostate volume, and PSA density (all <italic>p</italic>  &lt; 0.01). MRI regression was significantly more frequent in the dutasteride group (64.1% vs. 35.1%, <italic>p</italic>  = 0.009), whereas pathological progression also occurred more frequently (23.4% vs. 8.1%, <italic>p</italic>  = 0.048). Multivariable analysis identified dutasteride use, higher baseline PSA density, and smaller prostate volume as independent predictors of pathological progression. Conclusions Although dutasteride was associated with favorable biochemical changes and increased MRI regression, these findings did not reliably reflect histopathological stability. MRI improvement during dutasteride therapy should therefore be interpreted cautiously, and biopsy-based surveillance remains essential to avoid overlooking clinically significant disease progression. </p>