Background
Phase 3, double-blind, placebo-controlled. N=921 mCRPC with symptomatic bone metastases, no known visceral disease. Prior docetaxel, ineligible, or declined. Radium-223: bone-seeking alpha emitter. Updated analysis at 528 deaths.
Results
Interventions and follow up: Arm A: radium-223 50 kBq/kg IV q4wk ×6 + best standard of care.
Arm B: matching placebo q4wk ×6 + best standard of care.
Randomization: 2:1 favoring radium-223.
Primary endpoint: overall survival; interim prespecified at 314 deaths, stopped early for efficacy.
mFollow up: NR.
Results: OS (updated): 14.9 vs 11.3 mo, HR 0.70, 95% CI 0.58–0.83, P<.001.
OS (interim): 14.0 vs 11.2 mo, HR 0.70, 95% CI 0.55–0.88, P=.002.
Time to first symptomatic skeletal event: 15.6 vs 9.8 mo, HR 0.66, P<.001.
Subgroups: benefit consistent across prior-docetaxel strata; all main secondary endpoints favored radium-223.
Arm B: matching placebo q4wk ×6 + best standard of care.
Randomization: 2:1 favoring radium-223.
Primary endpoint: overall survival; interim prespecified at 314 deaths, stopped early for efficacy.
mFollow up: NR.
Results: OS (updated): 14.9 vs 11.3 mo, HR 0.70, 95% CI 0.58–0.83, P<.001.
OS (interim): 14.0 vs 11.2 mo, HR 0.70, 95% CI 0.55–0.88, P=.002.
Time to first symptomatic skeletal event: 15.6 vs 9.8 mo, HR 0.66, P<.001.
Subgroups: benefit consistent across prior-docetaxel strata; all main secondary endpoints favored radium-223.
Adverse events
Hematologic: G3/4 thrombocytopenia 6% vs 2%, neutropenia 3% vs 1%; anemia mostly low grade.
GI: diarrhea, nausea, vomiting.
Overall: low myelosuppression; fewer serious AEs than placebo.
GI: diarrhea, nausea, vomiting.
Overall: low myelosuppression; fewer serious AEs than placebo.
Conclusions
Radium-223 prolonged OS and delayed symptomatic skeletal events in symptomatic bone-met mCRPC with low toxicity; first bone-targeted alpha emitter to extend survival.
Key Limitations
Enrolled 2008–2011 when docetaxel was the only life-prolonging systemic option; modern ARPIs not represented. Visceral metastases excluded, limiting generalizability. Critically, do NOT combine radium-223 with abiraterone — ERA-223 showed increased fractures and deaths with that combination.
Clinical Context
FDA-approved 2013 (EMA 2013) for symptomatic bone-predominant mCRPC without visceral disease. ASCO and ESMO guidelines endorse radium-223 as a life-prolonging option in this setting, used as monotherapy with bone-protective agents. Sequenced among ARPIs, taxanes, and PSMA-targeted radioligand therapy.