Re-treatment with radium-223 is well tolerated and continues to control disease progression in bone in men with castration-resistant prostate cancer (CRPC) and bone metastases, according to study findings presented at the 2016 Genitourinary Cancers Symposium in San Francisco.

Based on a study of 44 CRPC patients who completed an initial 6-injection course of treatment with radium-223, a research team led by Oliver Sartor, MD, of the Tulane Cancer Center in New Orleans, found that radiographic bone progression with radium-223 re-treatment was rare, with most disease progression occurring in soft tissue.

Of the 44 patients, 29 (66%) completed re-treatment with all 6 injections. The median time from the end of initial radium-223 treatment was 6 months. Thirty-two patients (73%) had failed prior treatment with newer hormonal agents, such as abiraterone or enzalutamide.

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The median time to radiographic bone progression was not reached. The median radiographic progression-free survival (rPFS) was 9.9 months. Of the 13 patients with rPFS events, 8 had soft tissue tumor progression, 2 had radiographic progression from disposition but not documented in radiographic tumor progression, 2 died, and 1 had confirmed radiographic bone progression.

Radium-223 is the first FDA approved alpha-emitting radiopharmaceutical. The drug selectively targets bone metastases and is approved for use in CRPC patients with symptomatic bone metastases. The safety and efficacy of radium-223 was established in the pivotal ALSYMPCA trial, which showed that treatment with the drug prolonged overall survival by a median of 3.6 months and significantly reducing the risk of death by 30%. In the trial, the dosing regimen was 1 injection every 4 weeks for a total of 6 injections. Radium-223 treatment beyond 6 injections has not been previously reported.

Dr. Sartor and his colleagues identified no marked alterations in treatment-emergent adverse event (TEAE) incidence compared with the ALSYMPCA trial. Only 2 re-treated patients experienced grade 3 hematologic TEAEs. No patients experienced grade 4 or 5 hematologic TEAEs.