External beam radiation therapy improves survival in elderly metastatic prostate cancer patients with low PSA

Background: It is unknown, whether metastatic prostate cancer (CaP) patients with intermediate life expectancy (5–10 years) should be considered for external beam radiation therapy (EBRT) to the prostate. We addressed this void. Methods: Within the Surveillance, Epidemiology, and End Results database (2004–2016), we identified 835 M1a or M1b CaP substaged patients with prostate-specific antigen (PSA) < 20 ng/ml and with intermediate life expectancy (LE) 5 to 10 years, treated with EBRT or no EBRT. Inverse probability of treatment-weighting (IPTW), Kaplan-Meier plots and Cox-regression models (CRMs) were used. Results: Overall, 179 (21.4%) patients received EBRT and 656 (78.6%) did not. EBRT rates increased from 13.9 to 23.8% (2004–2016; P= 0.04). After IPTW-adjustment, median OS was 45 vs. 35 months, in EBRT vs. no EBRT patients (P < 0.001). In IPTW-adjusted Cox-regression models, EBRT independently predicted lower overall mortality (hazard ratio [HR]: 0.7, CI 0.61–0.89; P= 0.001). After stratification according to M1 substages, EBRT was associated with lower overall mortality in M1a (HR: 0.2, CI 0.05–0.91; P= 0.03) and M1b (HR: 0.7, CI 0.55–0.88; P = 0.003) substages. Conclusion: EBRT was associated with lower mortality in metastatic CaP patients with low PSA and intermediate LE (5–10 years). In consequence, greater consideration for EBRT should be given in those patients. However, it is important to consider study limitations until clinical trials confirm the proposed benefit.