Timo Soeterik

120 CHAPTER 7 ABSTRACT Background : Prediction of side-specific extraprostatic extension (EPE) is crucial in selecting patients for nerve sparing radical prostatectomy (RP). The aim of this study is to develop and externally validate nomograms including multiparametric magnetic resonance imaging (mpMRI) information to predict side-specific EPE. Methods : A retrospective analysis of 1870 consecutive prostate cancer patients that underwent robot-assisted RP from 2014 to 2018 at three institutions was performed. Four multivariable logistic regression models were established, including combinations of patient-based and side-specific variables including: prostate-specific antigen (PSA)- density, highest ipsilateral biopsy International Society of Urological Pathology (ISUP) grade, ipsilateral percentage of positive cores on systematic biopsy and side-specific clinical stage assessed by both digital rectal examination and mpMRI. Discrimination (area under the curve [AUC]), calibration and net benefit of these models were assessed in the development cohort and two external validation cohorts. Results : On external validation, AUCs of the four models ranged from 0.80 (95% CI 0.68 – 0.88) to 0.83 (95% CI 0.72 – 0.90) in validation cohort 1 and from 0.77 (95% CI 0.62 – 0.87) to 0.78 (95% CI 0.64 – 0.88) in validation cohort 2. The three models including mpMRI staging information resulted in relatively higher AUCs compared with the model without mpMRI information. No major differences between the four models regarding net benefit were established. The model based on PSA-density, biopsy ISUP grade and mpMRI T-stage was superior in terms of calibration. Using this model with a cut-off of 20%, 1980/2908 (68%) of all prostatic lobes without EPE would be found eligible for nerve sparing, whereas non-nerve sparing would be advised in 642/832 (77%) lobes with EPE. Conclusions : Our analysis resulted in a simple and robust nomogram for the prediction of side-specific EPE which should be used to select patients for nerve sparing RP.