External validation of a nomogram for identification of pathologically favorable disease in intermediate risk prostate cancer patients

OBJECTIVE: To establish an external validation of the new nomogram from Gandaglia et al which provides estimates of the probability of pathological favorable disease in pre-operatively defined intermediate-risk PCa. PATIENTS AND METHODS: Overall, 2928 intermediate-risk PCa patients according to the D'Amico classification undergoing RP and bilateral lymph node dissection in seven academic centres between 2000 and 2011. Pathologically favorable PCa was defined as low-grade organ-confined disease. The Receiver Operating Characteristic (ROC) curve was obtained to quantify the overall accuracy (Area Under the Curve, AUC) of the model to predict specimen-confined (SC) disease. Calibration curve was then constructed to illustrate the relationship between the risk-estimates obtained by the model and the observed proportion of SC disease. Kaplan-Meier method was used for PSA recurrence-free survival (PSA-RFS) assessment. RESULTS: Median age was 68 years. 10.6% patients finally presented pathologically favorable disease characteristics at RP. A higher PSAD (OR = 0.01; 95%CI = 0.00-0.04; P < 0.0001) and percentage of positive cores (OR = 0.97; 95%CI = 0.96-0.98; P < 0.0001) were associated with a reduced probability of favorable disease at RP in multivariate analysis. ROC curve analysis showed strongest accuracy of the model (AUC = 0.82; 95%CI = 0.79-0.84). Favorable PCa had a significantly better PSA recurrence-free survival rates as compared to unfavorable PCa after RP (94.2% vs 74.4% at 4 years, P < 0.0001). CONCLUSIONS: This external validation of the Gandaglia nomogram shows relevant accuracy with one out of ten patients in this intermediate risk PCa group with pathologically proven organ-confined disease. This validated risk calculator can help physician to distinguish favorable intermediate risk PCa that can be treated by conservative approach or safer nerve-sparing surgery.