Updated Prostate Cancer Risk Groups by Prostate-specific Membrane Antigen Positron Emission Tomography Prostate Cancer Molecular Imaging Standardized Evaluation (PPP2): Results from an International Multicentre Registry Study

Abstract

Background and objective: We established prognostic nomograms incorporating prostate-specific membrane antigen (PSMA) positron emission tomography (PET) parameters standardised by Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE; PPP1). Here, we develop an updated PPP2 risk score from a large international multicentre registry study. Methods: We included 6128 prostate cancer patients who underwent PSMA-PET at 20 hospitals in Europe, USA, and Australia between 2013 and 2022. Investigator sites were split 2:1 into the development (4044 patients) and validation (2084 patients) cohorts. We created nomograms of version 2 (PPP2) based on Cox regression models with the least absolute shrinkage and selection operator penalty for overall survival (development cohort). Performance of both nomograms was measured using Harrell's C-index and calibration plots and a head-to-head comparison with the National Comprehensive Cancer Network (NCCN) risk score by receiver operating characteristic curves (validation cohort). Key findings and limitations: Predictors were distant metastases (extrapelvic nodal metastases [M1a], bone metastases [M1b], and visceral metastases [M1c]), PSMA expression score, and total lesion count (visual PPP2) or total tumour volume (quantitative PPP2). C-indices (95% confidence interval) in the validation cohort were 0.80 (0.78–0.82; visual) and 0.80 (0.79–0.82; quantitative), respectively. Accuracy of both the PPP2 nomograms was superior to the NCCN risk score (n = 1034, area under the curve 0.84 vs 0.76; p < 0.001). The retrospective design represents a limitation of the study. Conclusions and clinical implications: PPP nomograms were improved in an international multicentre study to predict accurately the 3- and 5-yr overall survival probabilities of prostate cancer. PPP2 yielded superior accuracy to the NCCN risk score. A free software tool has been created for PROMISE and PPP2 assessments (promise-pet.org).