Association between prostate radiotherapy and survival among patients with metastatic prostate cancer by extent of disease burden.

[BACKGROUND AND OBJECTIVE] Prostate radiotherapy (RT) is increasingly used in the treatment of hormone-sensitive metastatic prostate cancer (PCa) based on evidence of benefit in subsets with low disease volume. However, survival outcomes of patients with metastatic PCa receiving prostate RT across contemporary distributions of stage are less well understood.

[METHODS] Within the National Cancer Database (2004-2020), we identified individuals with de-novo metastatic PCa treated with hormonal therapy (HT) with or without prostate RT. Kaplan-Meier curves and multivariable proportional hazard regression models were used to compare overall survival (OS) across nodal (M1a), bone (M1b), and visceral (M1c) disease, using propensity score matched (PSM) samples.

[RESULTS] We identified 48,121 eligible patients, including 42,437 (88.2 %) patients receiving only HT and 5,684 (11.8 %) patients receiving HT + RT. In PSM-adjusted hazard regression models, RT was associated with improved OS (HR: 0.62; 95 % CI: 0.58-0.66; p < 0.001). The association differed by metastatic substage; the risk of death was reduced in patients with M1a (HR: 0.48; 95 % CI: 0.39-0.58; p < 0.001) and M1b disease (HR: 0.60; 95 % CI: 0.56-0.65; p < 0.001). No significant OS benefit was observed in M1c disease (HR: 0.91; 95 % CI: 0.74-1.13; p < 0.001).

[CONCLUSION] Prostate RT with HT was associated with improved survival in this observational study of patients with metastatic PCa. However, these associations differed by metastatic substage, with greater benefit in M1a, and no apparent benefit in M1c disease.In the era of molecular imaging, further refinement of patient selection for prostate RT may optimize treatment benefit.