Effects of six-cycle completion and earlier use of radium-223 therapy on prognosis for metastatic castration-resistant prostate cancer: A real-world multicenter retrospective study.

OBJECTIVES: To evaluate the effect of 6-cycle completion and earlier use of radium-233 dichloride (Ra223) on the prognosis of patients with metastatic castration-resistant prostate cancer (mCRPC). METHODS: We retrospectively evaluated 75 patients with bone metastases-predominant mCRPC who were treated with Ra223 between August 2016 and August 2021. The primary purpose of the study was to assess the effect of Ra223 completion (6 cycles) on patient prognosis, and the secondary purpose was to investigate factors associated with Ra223 incompletion (fewer than 6 cycles) and overall survival. RESULTS: The median age of the patients was 72 years. The median number of Ra223 administrations was 6 (interquartile range, 5-6), and the median Ra223 completion rate was 75%. The median time from mCRPC diagnosis to Ra223 administration was 17 months, and the median number of prior treatments was 2. Multivariable analysis indicated that unfavorable performance status (>0), prostate-specific antigen (PSA) level >10 ng/ml, extension of bone metastasis score 3 to 4, and Ra223 incompletion were significantly associated with poor overall survival. In addition, EOD 3 to 4 and 3 or more prior CRPC treatments were significantly associated with Ra223 incompletion. CONCLUSION: Six-cycle completion and earlier administration of Ra233 are potentially associated with favorable survival. Unfavorable factors (EOD 3-4 and ≥3 prior treatments) were significantly associated with Ra223 incompletion.