SAN FRANCISCO—A novel medication may provide a new standard of care for the treatment of patients with castration-resistant prostate cancer (CRPC) and bone metastases, researchers reported here at the annual Genitourinary Cancers Symposium.

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In a phase 3 study, radium-223 chloride—a first-in-class drug—significantly prolonged overall survival and time to first skeletal event (SRE) in CRPC patients with bone metastases, according to lead investigator Chris Parker, MD, of The Royal Marsden NHS Foundation Trust in Sutton, U.K. In addition, the drug was well tolerated and associated with a low incidence of myelosuppression.

“Radium-223 is chemically-speaking like calcium, so it localizes to bone, and specifically to bone metastases,” Dr. Parker said. “And radium-223 is an alpha emitter, so once in the bone it emits alpha particles, which are highly lethal and highly localized because they are very, very short range.”

He and his colleagues analyzed data from 809 patients randomized to receive radium-223 (541 men) or placebo (268 men). The primary endpoint was overall survival.

The median overall survival was 14 months in the radium-223 group compared with 11.2 months in the placebo recipients, which translated into a 30% decreased death risk. The median time to first SRE was 13.5 months in the radium-223 group versus 8.4 months in the placebo arm, a 39% reduction in SRE risk.

Radium-223 significantly reduced time to three of four SRE components: time to first use of external beam radiotherapy to relieve skeletal symptoms; time to first spinal cord compression; and time to first symptomatic pathologic bone fracture.

With respect to adverse events (AEs), grade 3 or 4 neutropenia was observed in only 2% of patients in the radium-223 arm and 1% of placebo recipients. Grade 3 or 4 thrombocytopenia was observed in 4% and 2% of these groups, respectively.

Sixty-eight patients (13%) in the radium-223 arm and 51 (20%) in the placebo group dropped out of the study because of AEs.

The symposium is cosponsored by the American Society of Clinical Oncology, the American Society of Radiation Oncology, and the Society of Urologic Oncology.