Radium-223 dichloride, an alpha emitter that targets bone metastases, reduces risk of death by 30 percent for men with castration-resistant prostate cancer and bone metastases, according to a study published July 18 in The New England Journal of Medicine.

The study also showed few adverse events for the group given radium-223 compared with a group receiving a placebo injection, reported Christopher Parker, MD, of the Royal Marsden National Health Service Foundation Trust and Institute of Cancer Research, Sutton, U.K., and colleagues.

Evidence of bone metastases is present in more than 90 percent of patients with metastatic castration-resistant prostate cancer, explained the authors. Radium-223 selectively binds to areas of increased bone turnover in bone metastases and emits high-energy alpha particles. “The highly targeted nature of radium-223, with alpha particles of short range (<100 μm), minimizes myelosuppression and has limited effects on normal tissue.”

To assess the efficacy and safety of radium-223, Parker and colleagues conducted the Alpharadin in Symptomatic Prostate Cancer Patients (ALSYMPCA) study. A total of 921 patients were randomly assigned in a 2:1 ratio to receive six injections of radium-223 or a placebo, with one injection administered every four weeks.

An interim analysis, conducted when 314 deaths had occurred, revealed median survival with radium-223 was 14 months, compared with 11.2 months for the placebo. A later analysis after 528 deaths had occurred confirmed the survival benefit, which had increased to an average of 3.6 months.

“All main secondary efficacy end points were significant and favored treatment with radium-223, including the clinically defined end point of the time to the first symptomatic skeletal event, which was significantly prolonged among patients who received radium-223,” wrote the authors.

Incidence of adverse events was consistently lower in the radium-223 group, and fewer members of the radium-223 group discontinued the study drug due to adverse events.

The study included both patients who had received the chemotherapy drug docetaxel and those who were not eligible or declined docetaxel. The authors noted that recent research has been conducted involving the use of cabazitaxel, abiraterone, and enzalutamide in patients who have received docetaxel, and they wrote that the safety profile of radium-223 suggests it is suitable to use with these other agents.