Potential effectiveness of local radiotherapy for extending survival and reducing symptomatic local events in patients with de novo metastatic prostate cancer

OBJECTIVES: To evaluate the association between the use of local radiotherapy (RT) with the survival of patients with de novo metastatic prostate cancer and symptomatic local events (SLEs). PATIENTS AND METHODS: Patients were initially diagnosed with metastatic prostate cancer between 2008 and 2017 at 30 institutes in Japan. Prostate‐specific antigen (PSA) progression‐free survival (PSA‐PFS) under initial androgen deprivation therapy and overall survival (OS) was compared between patients receiving local RT (RT group) and no RT (no‐RT group) by multivariate Cox proportional hazard analyses. The occurrence rate of grade ≥2 SLEs was compared by multivariate logistic regression analyses. Propensity score matching (PSM) analyses were performed to compare PSA‐PFS and OS of the groups in the high and low metastatic burden cohort. RESULTS: Two hundred and five (7%) of 2829 patients received RT before PSA progression. Median PSA‐PFS and OS were significantly longer in the RT group than in the no‐RT group and the difference was significant in multivariate analyses (HR = 0.44, 95% CI = 0.33‐0.57 and HR = 0.40, 95% CI = 0.27‐0.60, respectively). The occurrence rate of grade ≥2 SLEs was significantly lower in the RT group (2%) than the no‐RT group (9%) and the difference was significant in multivariate analyses (HR = 0.28, 95% CI = 0.10‐0.76). Using PSM analyses, PSA‐PFS and OS remained significantly different (HR = 0.64, 95% CI = 0.46‐0.89 and HR = 0.47, 95% CI = 0.30‐0.72, respectively), between the RT (n = 182) and the no‐RT (n = 182) groups. The difference in OS was significant in the high metastatic burden cohort (HR = 0.55, 95% CI = 0.37‐0.81). CONCLUSIONS: Addition of local RT to standard treatment for de novo metastatic prostate cancer patients tends to have the potential to extend survival, even in patients with high metastatic burden, and to reduce SLEs.