Lower Fracture Rates in Patients Treated with Radium-223, Abiraterone or Enzalutamide, When Given Concurrently with Bone Health Agents: A Real-World Analysis.

Background: The phase 3 trial ERA223 demonstrated an increased fracture rate and no survival advantage for metastatic castration resistant prostate cancer (mCRPC) patients on Radium-223 (Ra-223) with abiraterone, leading to regulatory restrictions on combination therapy. However, less than half of trial patients received bone health agents (BHA). We reviewed electronic health record (EHR) data evaluating fracture rates for patients on BHA receiving Ra-223, androgen deprivation therapy and either abiraterone or enzalutamide.

Patients And Methods: We conducted a retrospective, cohort analysis of EHR data of mCRPC patients on Ra-223 treated at a single community center by a single provider between 2010 and 2018. The primary objective was evaluating fracture rates for patients on BHA receiving Ra-223 and abiraterone. We conducted a secondary analysis for enzalutamide.

Results: One hundred seventy-seven patients received Ra-223 concurrently with abiraterone or enzalutamide between November 2010 and August 2018. The median age was 73 at first Ra-223 dose (range 40-93). The median follow-up time from last Ra-223 dose was 30 months (range 2-106). One hundred sixty-four patients (93%) received BHAs. One hundred fifty-nine patients (89%) were on a BHA before and/or during Ra-223. Sixty-seven patients received denosumab (38%), 63 received zoledronic acid (36%), and 29 received both nonconcurrently (16%). Eleven patients (6.2%) experienced a fracture after starting Ra-223, 9 of which occurred while on prior and/or concurrent BHA. We observed a 5.7% fracture rate for mCRPC patients who received combination therapy and denosumab or zoledronic acid.

Conclusion: This real-world analysis demonstrating a low fracture rate in patients with mCRPC receiving a BHA while on Ra-223 and abiraterone or enzalutamide may inform current clinical practice.