LAUSR

OBJECTIVE To assess the relationship between the volume of the index lesion (IL) measured at mpMRI (MRIvol) and at radical prostatectomy (RPvol), stratifying it according to PI-RADS score. MATERIALS AND METHODS We identified 332 men with a positive mpMRI (single lesion with PI-RADS≥3) who underwent systematic plus targeted biopsy and subsequent RP at two tertiary referral centres between 2013 and 2018. All mpMRI scan were reviewed by experienced radiologists using PI-RADS score. The study outcome was to assess the relationship between MRIvol (based on planimetry from MRI sequence best showing tumor) and RPvol (based on tumor involved area of each RP pathology slice). To achieve this endpoint, we performed a multivariable linear regression analysis (LRA) to predict RPvol using PI-RADS, PSA, prostate volume, age, DRE, Gleason score at MRI-targeted biopsy, biopsy history and time from mpMRI to RP as covariates. Non-parametric loess function was used to graphically explore the relationship between MRIvol and RPvol, stratifying for PI-RADS score. RESULTS Overall, 24%, 49% and 27% of men had a visible PI-RADS 3, 4 and 5 lesion at mpMRI. The median MRIvol and RPvol were 0.67 cc (interquartile range [IQR]: 0.29-1.76) and 1.39 cc (IQR: 0.58-4.23). At LRA, MRIvol was significantly correlated with a RPvol underestimation (slope: 2.4, 95% confidence interval [CI]: 0.1-46.3). The non-parametric loess analysis showed a non-linear relationship between MRIvol and RPvol. Significant underestimation was reported across all volumes with the highest differences between MRIvol and RPvol in the low volume range (<2 cc), where RPvol almost doubled MRIvol. A similar effect was observed across all PI-RADS scores subgroups. CONCLUSIONS mpMRI significantly underestimates the exact volume of the IL, especially for small visible lesions, regardless of PI-RADS score. This should be taken into account when planning tailored focal therapy approaches often delivered to men with smaller prostatic lesions.