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

e17123 Background: Because of improved oncologic efficacy, external beam radiotherapy (RT) is increasingly used in men with metastatic hormone-sensitive prostate cancer (mHSPC). Despite evidence in support of RT demonstrating improved outcomes in the low-burden prostate metastatic disease, survival outcomes of men with mHSPC receiving RT in the real-world treatment setting, including higher burdens of disease, are less well understood. Methods: We conducted a retrospective analysis of the National Cancer Database to identify individuals newly diagnosed with metastatic prostate cancer, all of whom were treated with androgen deprivation therapy (ADT). Patients were separated into two groups based on their treatment modalities: ADT and ADT+RT. Kaplan-Meier curves, Cox proportion hazard models, and log-ranked tests were estimated to compare overall survival, stratified by treatment modality, for prostate cancer metastases to the lymph nodes (M1a), bone (M1b), and visceral organs (M1c). Significance threshold was set at p<0.05. Results: We identified 67,263 eligible patients with mHSPC diagnosed from 2004 through 2020, including 4,543 (6.8%) patients with M1a, 50,340 patients (74.8%) patients with M1b, and 12,380 (18.4%) patients with M1c disease. The association between radiation therapy and overall survival was moderated by metastatic stage (interaction p-value < 0.001). Among the subset of individuals with M1a disease, the addition of RT to ADT was associated with improved overall survival on multivariable analysis (hazard ratio, 0.61; 95% CI, 0.50 to 0.75) adjusted for age, race, ethnicity, comorbidity score, Gleason grade group, T stage, N stage, treating facility, and insurance status. For individuals with M1b disease, RT showed no significant effect on overall survival (HR = 1.00, 95% CI: 0.91–1.11). Conversely, for individuals with M1c disease, RT was associated with poorer overall survival (HR = 1.30, 95% CI: 1.14–1.48). Conclusions: This retrospective study identified differences in overall survival by receipt of prostate radiation therapy by metastatic cancer stage. These findings favor improved outcomes in low disease burden (M1a) disease and may suggest opportunities to further identify subsets that favor primary local therapy.