Abstract 3920: Tumor volume as a predictor of lymph node metastases in prostate cancer

Introduction: Pelvic lymph node dissection (PLND) is recommended during radical prostatectomy (RP) in patients with high risk prostate cancer (PCa). Guidelines recommend extended PLND in patients who have >5% probability of lymph node involvement, calculated from pre-operative parameters. PLND increases procedure time and potential morbidity to patients. Tumour size has been reported to be predictive of biochemical recurrence after RP. We analysed the utility of several parameters including tumour size in predicting lymph node metastases in order to further refine the population who require PLND during RP. Materials & Methods: We maintained a prospective database of Robotic Assisted Radical Prostatectomy (RARP) from July 2012 to August 2016 consisting of a cohort of 531 patients. Patients with >5% calculated probability of lymph node metastasis had PLND during RARP. We performed multiple linear regression using age, PSA, D’Amico risk score, ISUP prognostic group, clinical T-stage, radiological T-stage, tumour volume, tumour volume relative to prostate size (relative tumour volume), and number of nodes excised during PLND to determine if any of these parameters could predict the presence of lymph node metastases. Results: Of the cohort of 531 patients, 154 had PLND during RARP. Of the PLND cohort, 15 (10%) had pN1 disease. Tumour volume (r2 0.044, p= 0.0098), relative tumour volume (r2 0.033, p=0.026) and number of lymph nodes excised (r2 0.046, p=0.0075) were independent predictors of pN1 disease. D’Amico risk score (r2 0.019, p=0.089) approached but did not reach statistical significance. Patients with pN1 disease all had primary tumours ≥6cc. Conclusions: In our cohort of PLND patients, tumour volume was an independent risk factor for pN1 disease. With the increasing availability of multi-parametric MRI, tumour volume can be measured pre-operatively as an adjunct to PIRADS scoring. The role of tumour volume and relative tumour volume in predicting lymph node metastasis in conjunction with other pre-operative parameters requires further investigation. The use of tumour volume in determining the need for PLND in patients undergoing RP may help to further refine the population at highest risk for pN1 disease and avoid the additional morbidity of PLND in those at low risk. In addition, our findings support the recommendation of performing an extended PLND to maximise regional lymph node clearance. Citation Format: Chidi N. Molokwu, Keith Yuen, Sanjay Addla, Rajindra Singh, Rohit Chahal. Tumor volume as a predictor of lymph node metastases in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3920. doi:10.1158/1538-7445.AM2017-3920