External validation of Memorial Sloan Kettering Cancer Center nomogram and prediction of optimal candidate for lymph node dissection in clinically localized prostate cancer

INTRODUCTION: The aim of our study was to evaluate the external validity of the online Memorial Sloan Kettering Cancer Center (MSKCC) nomogram as a predictor for pelvic lymph node invasion (LNI) in men who underwent radical prostatectomy (RP) with pelvic lymph node dissection (PLND). MATERIAL AND METHODS: The study cohort consisted of 679 men with clinically localized prostate cancer (PCa) who underwent RP with PLND between 2005 and 2017. The area under curve (AUC) of the receiver operator characteristic analysis was used to quantify the accuracy of MSKCC nomogram to predict LNI. The specificity, sensitivity and negative predictive value were calculated to assess LNI probability cut-off. RESULTS: A total of 81 of 679 patients had LNI (11.9%). The AUC of MSKCC nomogram was 79%. Using the cut-off value of 7% (sensitivity 88.9%, specificity 45.2% and NPV 96.8%) a PLND could be omitted in 41% (279/679) of men. However, 3.2% (9/279) of men with LNI would be missed. MSKCC nomogram showed good calibration characteristics and high net benefit at decision curve analysis. CONCLUSIONS: MSKCC nomogram in patients with PCa undergoing PLND has 79% discriminated accuracy for prediction of LNI in our cohort. Using a 7% nomogram cut-off, roughly 40% of men would be spared PLND with minimal risk to miss LNI.