Timo Soeterik

86 CHAPTER 5 ABSTRACT Background: Available published studies evaluating the association between nerve sparing robot-assisted radical prostatectomy (RARP) and risk of ipsilateral positive surgical margins were subject to selection bias. In this study we aim to overcome these limitations by using multivariable regression analysis. Methods: Patients undergoing RARP for prostate cancer at 4 institutions from 2013 to 2018 were included in the study. A multilevel logistic random intercept model, including covariates on patient level and side-specific factors on prostate lobe level, was used to evaluate the association between nerve sparing and risk of ipsilateral positive margins. Results: A total of 5148 prostate lobes of 2574 patients who underwent RARP were analysed. Multivariable analysis showed nerve sparing was an independent predictor for ipsilateral positive margins (OR 1.42, 95% CI 1.14 - 1.82). Other significant predictors for positive margins were prostate specific antigen density (OR 3.64, 95% CI 2.36 - 5.90) and side-specific covariates including highest preoperative biopsy International Society of Urological Pathology (ISUP) grade (OR 1.58, 95% CI 1.13 - 2.53; OR 1.62, 95% CI 1.13 - 2.69; OR 2.11, 95% CI 1.39 - 3.59 and OR 4.43, 95% CI 3.17 - 10.12 for ISUP grade 2, 3, 4 and 5, respectively), presence of extraprostatic extension on magnetic resonance imaging (OR 1.42, 95% CI 1.03 - 1.91) and percentage of positive cores on systematic biopsy (OR 3.82, 95% CI 2.50 - 5.86). Conclusions: Nerve sparing was associated with an increased risk of ipsilateral positive surgical margins. The increased risk of positive margins should be taken into account when counselling patients who opt for nerve sparing RARP.