Overall survival benefit and safety profile of radium-223 chloride, a first-in-class alpha-pharmaceutical: Results from a phase III randomized trial (ALSYMPCA) in patients with castration-resistant prostate cancer (CRPC) with bone metastases.

Abstract

8 Background: Radium-223 chloride (Ra-223) is a first-in-class alpha-pharmaceutical targeting bone metastases (mets) with high-energy alpha-particles of extremely short range (<100 μm). ALSYMPCA, a phase III, double-blind, randomized, multinational study, compared efficacy, in terms of overall survival (OS), and safety of Ra-223 plus best standard of care (BSC) vs placebo plus BSC in patients (pts) with bone mets in CRPC. Methods: Eligible pts had progressive, symptomatic CRPC with ≥ 2 bone mets on scintigraphy and no known visceral mets; were receiving BSC; and either previously received docetaxel, were docetaxel ineligible, or refused docetaxel. Pts were randomized 2:1 to receive 6 injections of Ra‐223 (50 kBq/kg IV) q4 wks or matching placebo and stratified by prior docetaxel use, baseline alkaline phosphatase level, and current bisphosphonate use. A planned interim analysis (IA) was conducted to assess the effect of Ra-223 on the primary endpoint (OS) using a predefined threshold. Survival data were compared using a stratified log-rank test. Results: 922 pts (Ra-223, n = 615; placebo, n = 307) were randomized from 6/2008-2/2011. 445 (58%) of 809 pts in the IA data set received prior treatment with docetaxel. Ra-223 significantly improved OS in pts with CRPC with bone mets vs placebo (two-sided P = 0.00185; HR = 0.695; 95% CI, 0.552-0.875; median OS 14.0 mo vs 11.2 mo, respectively). Safety and tolerability of Ra-223 were highly favorable and showed low incidence of myelosuppression (eg, grades 3/4 neutropenia in 1.8% and 0.8% and thrombocytopenia in 4% and 2% of the Ra-223 and placebo groups, respectively). Conclusions: Ra-223 is an effective therapy that improved OS with a highly favorable safety profile, and may provide a new standard of care for the treatment of CRPC pts with bone mets. [Table: see text]