Surgical margins and biochemical recurrence risk at 2 years for robotic prostatectomy: Comprehensive evaluation and CUSUM analysis of oncological outcomes.

Abstract

80 Background: To evaluate the learning curve of Minimally Invasive Radical Prostatectomy (MIRP) in our institution and apply the cumulative summation (CUSUM) analytical technique to identify salient learning curve transition points in terms of oncological outcomes. Methods: Clinical, pathologic, and oncological outcome data were collected from our prospectively collected MIRP database to estimate Positive Surgical margin (PSM) and Biochemical Recurrence (BCR) trends during a 15 year period from 1998 to 2013. All the RPs (laparoscopic (LRP) / Robotic Assisted [RARP]) were performed by 9 surgeons. PSM was defined as presence of cancer cells at inked margins. BCR was defined as serum Prostate Specific Antigen (PSA) >0.2 ng/ml and rising or start of secondary therapy. Surgical learning curve was assessed with the application of Kaplan-Meier curves, Cox regression model, CUSUM and logistic model in order to define the “transition point” of surgical improvement. Results: We identified 5,547 patients with localized prostate cancer treated with MIRP (3,846 - LRP and 1,701 – RARP). Patient characteristics of LRP and RARP were similar. The overall risk of PSM in LRP was 25%, 20% and 17% for the first 50, 50 to 350 and >350 cases, respectively. For the same population, the 5-year BCR rate decreased from 21.5% to 16.7%. RARP started 3 years after the LRP program (after approximately 250 LRP). The PSM rate for RARP decreased from 21.8% to 20.4% and the corresponding 5-year BCR rate decreased from 17.6% to 7.9%. The CUSUM analysis showed significantly lower PSM and BCR at 2 years occurred at the transition point of 350 cases for LRP and 100 cases for RARP. In multivariable analysis, predictors of BCR were PSA, Gleason score, extra prostatic disease, seminal vesicle invasion and number of operations (p < 0.05). Patients harboring PSM showed higher BCR risk (23% vs. 8%, p < 0.05). Conclusions: Learning curve trends of MIRP in our large, single center experience showed significant reduction in PSM and BCR risk at 2 years are noted after the initial 350 cases and 100 cases of LRP and RARP, respectively.