(ChemotherapyAdvisor) – Radium-223 dichloride (Ra-223) is associated with significant improvements in overall survival (OS) among patients with castration-resistant prostate cancer (CRPC) and bone metastases, and could represent a new standard of care for these patients, according to authors of a new analysis from the double-blind, randomized, multinational, phase 3 ALSYMPCA study, presented at the 2013 Genitourinary Cancers Symposium in Orlando, FL.

The United States Food and Drug Administration (FDA) granted Ra-223 fast-track “priority review” status this month.

“Ra-223 significantly improved OS in CRPC patients with bone metastases by a median increase of 3.6 months compared with placebo (median OS: 14.9 vs. 11.3 months; < 0.001; HR, 0.69; 95% CI: 0.58-0.83),” reported lead author Nicholas J. Vogelzang, MD, at the Comprehensive Cancer Centers of Nevada, in Las Vegas, NV, and coauthors. “Ra-223 is an effective therapy with a highly favorable safety profile and may provide a new standard of care for treatment of CRPC patients with bone metastases.”

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Ra-223 “significantly delayed” times to first skeletal-related events (SREs), Dr. Vogelzang and his coauthors added. “Despite the longer time at risk, Ra-223 patients had an approximately 50% reduction in risk for spinal cord compression.”

The study enrolled a total of 921 patients with progressive, symptomatic CRPC, two or more metastatic bone tumors (detected on scintigraphy), and no visceral metastatic tumors. Forty percent of patients had more than 20 metastatic bone tumors.

“Patients were randomized 2:1 to receive six injections of Ra‑223 (50 kBq/kg IV) every 4 weeks or matching placebo and stratified by prior docetaxel use, baseline alkaline phosphatase level, and current bisphosphonate use,” the authors explained.

“Ra-223 significantly delayed time to first SRE versus placebo by a median increase of 5.8 months (median time to SRE: 15.6 vs. 9.8 mo; < 0.001; HR, 0.66; 95% CI: 0.52-0.83),” the researchers reported. “Ra-223 also reduced the risk of time to first event for all four SRE components versus placebo.” 

Ra-223, previously referred to as radium-223 chloride, is a first-in-class investigational alpha particle-emitting agent that has not yet been approved by the FDA but is under development for use with CRPC patients with bone metastases. It emits high-energy, short-range (< 100 μm) alpha particles.

Ra-223 was granted priority review status by the FDA earlier this month. The agency grants priority review status to medicines that offer treatments for patients with few or no adequate therapy options; the goal of the designation is to fast-track regulatory review for completion within 6 months of the submission of the new drug application (NDA). The US Nuclear Regulatory Commission approved licensing of Ra-223 in January 2013 to allow medical facilities in the United States to procure and administer the agent.

The 2013 Genitourinary Cancers Symposium is co-sponsored by the American Gastroenterological Association (AGA) Institute, the American Society of Clinical Oncology (ASCO), the American Society for Radiation Oncology (ASTRO) and the Society of Urologic Oncology (SUO).

Clinical trial information: NCT00699751