Radium-223 Safety, Efficacy, and Concurrent Use with Abiraterone or Enzalutamide: First U.S. Experience from an Expanded Access Program.

BACKGROUND: In the phase III ALSYMPCA trial, metastatic castration-resistant prostate cancer (mCRPC) patients had few prior life-prolonging therapies. Following ALSYMPCA, which demonstrated radium-223 survival benefit, and before radium-223 U.S. commercial availability, an expanded access program (EAP) providing early-access radium-223 allowed life-prolonging therapies in current use.

SUBJECTS, MATERIALS, AND METHODS: This phase II, open-label, single-arm, multicenter U.S. EAP (NCT01516762) enrolled patients with symptomatic mCRPC, ≥2 bone metastases, and no lung, liver, or brain metastases. Patients received radium-223 55 kBq/kg intravenously every 4 weeks × 6. Primary outcomes were acute and long-term safety. Additional analyses were done by number of radium-223 injections, and prior or concomitant abiraterone or enzalutamide use.

RESULTS: Of 252 patients, 184 received radium-223: 165/184 (90%) had Eastern Cooperative Oncology Group (ECOG) performance status 0-1; 183 (99%) had prior systemic anticancer therapy. Treatment-related adverse events occurred in 93/184 (51%) patients during treatment and 11 (6%) during follow-up. Median overall survival was 17 months, with 134/184 (73%) patients censored because of short follow-up due to radium-223 approval. In post hoc analyses, patients with ≥3 prior anticancer medications, baseline ECOG performance status ≥2, and lower baseline hemoglobin were less likely to receive 5-6 radium-223 injections and unlikely to benefit from radium-223. Radium-223 was well tolerated regardless of concurrent or prior abiraterone or enzalutamide.

CONCLUSION: Radium-223 was well tolerated, with no new safety concerns; safety was maintained with abiraterone or enzalutamide. Patients with more advanced disease were less likely to benefit from radium-223. Clinicians should consider baseline characteristics and therapy sequence for greatest clinical value.

IMPLICATIONS FOR PRACTICE: In this phase II U.S. expanded access program, radium-223 was well tolerated, with a median overall survival of 17 months in metastatic castration-resistant prostate cancer patients. In post hoc analyses, radium-223 was safe regardless of concurrent abiraterone or enzalutamide, and median overall survival appeared longer when radium-223 was used earlier in patients with less prior treatment. Patients with more advanced disease were less likely to benefit from radium-223. Clinicians should consider baseline clinical characteristics and therapy sequence to provide the greatest clinical value to patients.