Concurrent or layered treatment with radium-223 and enzalutamide or abiraterone/prednisone: real-world clinical outcomes in patients with metastatic castration-resistant prostate cancer

BACKGROUND: In this study, we evaluated real-world data on radium-223 plus abiraterone/prednisone or enzalutamide. Previously, the ERA 223 trial (NCT02043678) demonstrated increased fracture risk with concurrent treatment with radium-223 and abiraterone plus prednisone/prednisolone in patients with metastatic castration-resistant prostate cancer (mCRPC). METHODS: We used the Flatiron Health database to perform a retrospective study of patients with mCRPC treated with radium-223. Treatment with radium-223 plus abiraterone/prednisone or enzalutamide was defined as concurrent if both drugs started within 30 days of one another, or layered when the second drug started ≥30 days after the first. The index date was defined as the day of the first radium-223 dose. Outcome measures included symptomatic skeletal events (SSEs), overall survival (OS), and patterns of treatments received. RESULTS: Of the 625 patients treated with radium-223, 22% received it together with abiraterone/prednisone and 27% with enzalutamide. When these agents were combined, they were often initiated in a layered fashion (73% layered, 23% concurrent). Prior or concomitant bone health agents (BHAs) were received by 67% and 55% of patients, respectively. Median follow-up was 9 months. Overall, incidence rates for SSEs and pathologic fractures were 0.35 and 0.11 patients per person-year, respectively. Median OS from mCRPC diagnosis was 28.1 months. CONCLUSIONS: In this real-world setting, combination treatments with radium-223 and abiraterone/prednisone or enzalutamide were common. These agents were more commonly given in a layered than a concurrent fashion. Incidence rates for SSEs were reduced when BHAs were used; however, BHAs were underutilized.