A prospective observational registry evaluating clinical outcomes of Radium‐223 treatment in a nonstudy population

The ALSYMPCA study established a 3.6 month Overall Survival (OS) benefit in metastatic Castration Resistant Prostate Cancer (mCRPC) patients treated with Radium‐223 dichloride (Ra‐223) over placebo. Here we report clinical outcomes of Ra‐223 treatment in a nonstudy population. In this prospective registry, patients from 20 Dutch hospitals were included prior to Ra‐223 treatment. Clinical parameters collected included previous treatments and Adverse Events. Primary outcome was 6 months Symptomatic Skeletal Event (SSE)‐free survival, while secondary outcomes included Progression‐Free Survival (PFS) and Overall Survival (OS). Of the 305 patients included, 300 were evaluable. The mean age was 73.6 years, 90% had ≥6 bone metastases and 74.1% were pretreated with Docetaxel, 19.5% with Cabazitaxel and 80.5% with Abiraterone and/or Enzalutamide. Of all patients, 96.7% were treated with Ra‐223 and received a median of 5 cycles. After a median follow‐up of 13.2 months, 6 months SSE‐free survival rate was 83%, median PFS was 5.1 months and median OS was 15.2 months. Six months SSE‐free survival rate and OS were comparable with those reported in ALSYMPCA. “Previous Cabazitaxel treatment” and “bone‐only metastases” were independent predictors of a shorter and longer PFS, respectively, while above‐median LDH and “bone‐only metastases” were independent predictors of shorter and longer OS, respectively. Toxicity was similar as reported in the ALSYMPCA trial. These results suggest that in a nonstudy population, Ra‐223 treatment is well‐tolerated, equally effective as in the ALSYMPCA population and that patients not previously treated with Cabazitaxel benefit most from Ra‐223.