First interim results of the Radium-223 (Ra-223) reassure observational study in metastatic castration-resistant prostate cancer (mCRPC): Safety and baseline (BL) characteristics of U.S. patients (Pts) by prior/concomitant treatment (Tx).

Abstract

233 Background: Ra-223, a targeted alpha therapy, extended survival and had a favorable safety profile at 3 years’ follow up in pts with mCRPC in the pivotal phase 3 ALSYMPCA trial. The maturing global, prospective, single-arm, observational REASSURE study, designed to evaluate long-term safety at 7 years’ follow up, enrolled pts with mCRPC with bone metastases planned to receive Ra-223. Methods: We performed a descriptive analysis of safety and BL characteristics of US pts according to prior or concomitant abiraterone/enzalutamide (abi/enza) or prior docetaxel/cabazitaxel (chemo) using data from the first planned interim analysis (pts receiving ≥1 Ra-223 dose; median follow up 8 mo). Results: 244 US pts were included; 80% had no prior chemo. Prior abi/enza and/or chemo pts had higher median BL PSA and were less likely to complete 5-6 doses (Table). Subgroups had similar median ALP, LDH and Hb. Overall, drug-related tx-emergent AEs occurred in 71 pts (29%) and serious AEs in 9 (3.7%). Most common AEs were diarrhea, fatigue and anemia. AE incidence was numerically higher in pts who received prior chemo and/or abi/enza. Clinical trial information: NCT02141438. Conclusions: To date, REASSURE has not revealed any new safety findings and most pts complete 5-6 Ra-223 doses in routine US clinical practice. Pts with prior tx lines had lower Ra-223 tx completion and higher AE incidence, likely reflecting greater disease burden, as evidenced by higher median BL PSA.[Table: see text]