Multicenter, international, retrospective study of prognostic factors for Ra223

The risk factors for adium-233 dichloride (Ra223) treatment on prognosis remain unclear.　We aimed to validate the risk model for a radium-233 dichloride (Ra223) on the prognosis of patients with metastatic castration-resistant prostate cancer (mCRPC). We retrospectively evaluated 345 patients with bone metastases-predominant mCRPC who were treated with Ra223 between August 2016 and October 2023 in Japan and Tiwan (R2D2 study). The primary purpose of the study was to validate the risk model for poor overall survival (OS) and Ra223 6-cycle incompletion. The secondary purpose was development of an international risk model. The risk model for poor OS included three factors: poor performance status, Ra223 6-cycle incompletion, and prostate specific antigen > 10 ng/mL. The risk model for Ra223 6-cycle incompletion included two factors: prior mCRPC treatments > 2 and extend of bone metastasis (EOD) 3-4. Of 345, we selected 71 and 274 patients with mCRPC for the development and validation cohorts, respectively. The number of risk factors (0-1 vs. 2-3) was significantly associated with for poor OS after Ra223 and OS after mCRPC diagnosis in the validation cohort. Our observation suggests that those factors may associate with favorable survival in patients treated with Ra223.