4-Year PSA Response Rate as a Predictive Measure in Intermediate Risk Prostate Cancer Treated With Ablative Therapies: The Sprat Analysis

Abstract

There is a lack of early predictive measures of outcome for patients with intermediate-risk prostate cancer (PCa) treated with stereotactic body radiotherapy (SBRT). We aim to explore 4-year PSA response rate (4yPSARR) as an early predictive measure.Individual patient data from 6 institutions for patients with intermediate-risk PCa treated with SBRT between 2006 and 2016 with a 4-year (42-54 months) PSA available were analyzed. Cumulative incidences of biochemical failure and metastasis were calculated using Nelson-Aalen estimates and overall survival was calculated using the Kaplan-Meier method. Biochemical failure-free survival was analyzed according to 4yPSARR with groups dichotomized based on PSA < 0.4 ng/mL or ≥ 0.4 ng/mL and compared using the log-rank test. Multivariable competing risk analysis was performed to predict for biochemical failure and development of metastasis.Six-hundred thirty-seven patients were included, including 424 (67%) with favorable and 213 (33%) with unfavorable intermediate-risk disease. Median follow-up was 6.2 years (IQR 4.9-7.9). The cumulative incidence of biochemical failure and metastasis, and overall survival at 6 years was 7%, 0.6% and 97%, respectively. The cumulative incidence of biochemical failure at 6 years if 4yPSARR < 0.4ng/mL was 1.7%, compared to 27% if 4yPSARR ≥ 0.4 ng/mL (P < 0.0001). On multivariable competing risk analysis, 4yPSARR was a statistically significant predictor of biochemical failure-free survival (sHR 15.3, 95% CI 7.5-31.3, P < 0.001) and metastasis-free survival (sHR 31.2, 95% CI 3.1-311.6, P = 0.003).4yPSARR is an encouraging early predictor of outcome in patients with intermediate-risk PCa treated with SBRT. Validation in prospective trials is warranted.