Prostate MRI and clinicopathologic risk calculator to predict laterality of extraprostatic extension at radical prostatectomy

Background: Traditional nomograms can inform the presence of extraprostatic extension (EPE) but not laterality, which remains important for surgical planning, and have not fully incorporated multiparametric MRI data. We evaluated predictors of side-specific EPE on surgical pathology including MRI characteristics and developed side-specific EPE risk calculators. Methods: This was a retrospective cohort of patients evaluated with mpMRI prior to radical prostatectomy (RP) in our eleven hospital healthcare system from July 2018-November 2022. The dominant side was defined pre-operatively using a tiered system based on laterality of highest biopsy Gleason Grade Group (GG), highest PIRADS lesion, number of lesions, and cancer volume. Univariable and multivariable logistic regression were performed for overall EPE, dominant side EPE, and non-dominant side EPE. Internal validation with leave one out and calibration curves were completed. Results: EPE was identified in 53% (317/601) of patients at RP. Side-specific factors (PIRADS, GG, abutment) were only associated with EPE on their respective side. Final variables in the model associated with EPE on the dominant and non-dominant sides included age, log PSA density (PSAD), side-specific PIRADS 5, side-specific GG3–5, and percentage positivity of systematic cores. AUCs for dominant and non-dominant side EPE were 0.77 (95% CI 0.73—0.80) and 0.79 (95% CI 0.74–0.84), respectively. MRI-identified abutment and prostate health index (PHI) did not improve model discrimination. Risk calculators available online at https://rossnm1.shinyapps.io/PredictionOfEPELaterality/. Conclusions: PSA, side-specific PIRADS, side-specific GG, and percentage positivity of systematic cores were associated with side-specific EPE at RP and incorporated into a risk calculator to assist in surgical planning and nerve-sparing decisions at time of RP.