Abstract
Abstract only 197 Background: Ra-223 tx for up to 6 injections (inj) is indicated for pts with symptomatic bone metastases. Ra-223 tx beyond 6 inj has not been previously reported. Herein we report the first safety and efficacy findings of Ra-223 re-tx from an international prospective trial in mCRPC pts. Methods: Pts with CRPC with ≥ 2 bone mets who completed 6 initial Ra-223 inj with no disease progression in bone and progressed after initial tx were potentially eligible for Ra-223 re-tx, provided that hematologic (heme) parameters were adequate. No concomitant cytotoxic agents were allowed; other agents were allowed at investigator discretion. Primary objective was safety. Exploratory objectives were time to radiographic bone progression, time to ALP progression, and radiographic progression-free survival (rPFS) based on MRI/CT and bone scans performed q 3 mo. Results: 44 pts had Ra-223 re-tx, 29 (66%) completed tx with all 6 inj; median (med) number inj = 6. Med time from initial Ra-223 tx = 6 mo. Besides prior Ra-223, all pts had ≥ 2 hormonal regimens; 45% had ≥ 1 chemotherapy regimen. 32 (73%) failed novel hormonal agents, eg, abiraterone and enzalutamide. Baseline characteristics were comparable to ALSYMPCA (Table). No new safety concerns were noted; incidence of tx-emergent adverse events (TEAEs) in re-tx pts was comparable to or lower than ALSYMPCA (Table). Only 2 re-tx pts had grade 3 heme TEAEs. Only 1 pt had radiographic bone progression; med time to ALP progression was not reached. Med rPFS = 9.9 mo. Conclusions: Ra-223 re-tx was well tolerated in this highly selected population, with minimal heme toxicity, and provided continued control of disease progression in bone. Clinical trial information: NCT01934790. [Table: see text] [Table: see text]