Radium-223 dichloride (radium-223), an alpha emitter with bone-seeking properties, is superior to placebo when used in combination with best standard of care in men with castration-resistant prostate cancer (CRPC) and bone metastases, according to a study published in the New England Journal of Medicine (2013;369:213-223).

Chris Parker, M.D., of the Royal Marsden Hospital in Sutton, U.K., and colleagues conducted a phase 3, randomized, double-blind trial in which 921 patients with CRPC and bone metastases were randomly assigned in a 2:1 ratio to either six injections of radium-223 or matching placebo. Patients had received, were not eligible to receive, or refused docetaxel therapy. All patients received the best standard of care. The primary end point was overall survival.

At a prespecified interim analysis involving 809 patients, the researchers found that median overall survival was 14 months in the patients treated with radium-223 compared with 11.2 months among placebo recipients, which translated into a significant 30% decreased risk of death. An updated analysis involving 921 patients also demonstrated significantly prolonged median overall survival with radium-223 compared with placebo (14.9 vs. 11.3 months). Rates of myelosuppression were low in patients receiving radium-223, and fewer adverse events were reported compared with those receiving placebo.

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“Radium-223 dichloride, the first alpha emitter to undergo phase 3 testing and receive approval for clinical use, acts independently of cell cycles, surface markers, and tumor types,” the authors of an accompanying editorial wrote. “The authors describe a well-executed international, multicenter trial showing an overall survival benefit associated with radium-223 in more than 900 patients with prostate cancer.”