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.