PCN31 REAL-WORLD TREATMENT PATTERNS OF RADIUM-223 IN PATIENTS WITH METASTATIC CASTRATION RESISTANT PROSTATE CANCER RECEIVING CARE AT A US TERTIARY ONCOLOGY CENTER

This study evaluated treatment patterns and outcomes among patients with metastatic castration resistant prostate cancer (mCRPC) treated with radium-223 in an academic clinical setting. A retrospective chart review study was conducted at Dana-Farber Cancer Institute of bone metastases-predominant mCRPC patients treated with radium-223 between 2013-2018. Treatment patterns, symptomatic skeletal events (SSE), and overall survival (OS) were measured. Outcomes were evaluated in patients receiving radium-223 pre- vs. post-chemotherapy. OS, defined from the time of mCRPC to death or last follow-up, was examined using Kaplan-Meier medians and 95% confidence intervals (CIs). 220 patients were treated with radium-223 (64 pre-chemotherapy, 83 post-chemotherapy, 73 no chemotherapy). Mean chemotherapy cycles received was 9.0 and 9.2 (pre- and post-chemotherapy); on average, radium-223 was given in the 3rd and 5th mCRPC line of therapy, pre- and post-chemotherapy (p<0.001). Among those who received radium-223 pre- vs. post-chemotherapy, 76.6% completed all 6 cycles of radium-223 vs. 46.3% (p<0.001). 92 (41.8%) patients were treated with radium-223 with another therapy, commonly abiraterone acetate (43.5%) and enzalutamide (52.2%). Overall, 122 (55.5%) patients received a bone-targeting agent following mCRPC, including zoledronic acid (31.4%) and denosumab (22.7%). 29 (13.2%) patients experienced an SSE post-radium-223. Median OS was 39.4 (95% CI 33.0, 48.8) vs. 37.4 months (95% CI 32.0, 43.5) for patients receiving radium-223 pre- vs. post-chemotherapy and 35.2 months (95% CI 27.9, 43.3) vs. 32.0 months (95% CI 26.9, 36.0) for patients receiving radium-223 in combination vs. monotherapy. While patients treated with radium-223 pre- vs. post-chemotherapy received similar cycles of chemotherapy, patients were more likely to complete all six cycles of radium-223 if treatment was administered pre-chemotherapy. OS was similar between groups receiving radium-223 pre- vs. post-chemotherapy and with or without combination hormonal therapy. Understanding real world treatment patterns of radium-223 use will be critical to optimizing therapy for patients.