Impact of Surgical Margins on Mortality after Robotic Radical Prostatectomy.

e17101 Background: Positive surgical margins (PSMs) following radical prostatectomy (RP) have long been seen as inherently unfavorable. Despite this belief, there has not been as much evidence supporting unifocal PSMs (UPSM) and prostate cancer-specific mortality (PCSM). Some have reported that multifocal PSM (MPSM) seems to be associated with PCSM. In this study, we examine and compare the impact on PCSM between percent tumor volume (PTV) and MPSMs. Methods: Prospectively collected data for 1552 patients with complete data who underwent RARP by a single surgeon between 2002 and 2018. The primary outcome was comparing risk of PCSM versus increasing pTV. Patients were categorized into pTV groups at a cutoff 40%. PSMs were categorized as negative (NSM), unifocal (UPSM), or multifocal (MPSM). Kaplan-Meier (KM) was used to assess time to OM and PCSM. Results: Men with 40-100% PTV were significantly older and had more advanced grades and stages. High PTV demonstrated a significantly greater risk of PSMs (both unifocal and multifocal), BCR, PCSM, and OM at 15 years. Before including PTV in the multivariate analysis, MPSM independently predicted PCSM, but UPSM did not. However, MPSMs lost their predictive significance when PTV was included. High-stage and Gleason grade group were independent predictors in both analyses. High PTV demonstrated shorter time to PCSM. Conclusions: Our study further challenges the common belief that PSMs are inherently oncologically adverse. Instead, MPSMs appear to signify more voluminous but more importantly aggressive underlying disease, which is the contributing factor for the adverse oncologic outcomes. We emphasize monitoring PTV as a key predictor of long-term adverse oncologic effects as a more reliable predictor of PCSM. Minimizing PSMs remains a critical surgical principle, but in prostate cancer, it needs to be weighed against urinary and sexual function outcomes.