Validation of the new STAR-CAP prognostic group staging system in prostate cancer patients treated with radiation therapy.

Abstract

To externally validate the STAR-CAP prognostic systemfor prostate cancer (PCa) and compare it to the CAPRA score to predict for biochemical recurrence (BCR) after radiation therapy (RTx). We included patients treated with RTx between 2002 and 2021 for non-metastatic PCa at our institution. BCR was defined based on Phoenix criteria. The 5-year BCR-free survival was assessed by univariable Kaplan-Meier analyses and log-rank test. Multivariable Cox regression models tested the independent association of each model for BCR. Performance of both models to predict 5-year BCR-free survival was assessed using the area under the curve (AUC). The 2768 patients included were treated with high dose rate brachytherapy (13.3%) as a boost to external beam radiation therapy (EBRT), low dose rate seed brachytherapy (50.4%) or EBRT alone (35.9%). 14.4% of patients received concomitant androgen deprivation therapy (ADT). 222 patients experienced BCR (8%), with a median follow-up of 56months. The 5-year BCR-free survival ranged from 88 (high risk) to 96% (low risk) in the STAR-CAP classification, and from 87 (high risk) to 97% (low risk) in the CAPRA system (p < 0.0001). Multivariate analyses, adjusted for ADT and type of treatment, confirmed the intrinsic ability of risk stratifications within each system to predict BCR (p < 0.001). Finally, AUC for the 5-year BCR prediction was 0.65 for STAR-CAP and 0.68 for CAPRA. Both CAPRA and STAR-CAP prognostic group staging systems provide sufficient stratification and their predictive ability for 5-year BCR-free survival is comparable, with a small advantage for CAPRA (3%).