Evaluation of clinical prognostic factors for radium-223 therapy in castration-resistant prostate cancer with bone metastases: the KYUCOG-1901 study

We evaluated clinical factors associated with symptomatic skeletal events (SSEs), radiographic progression-free survival (rPFS), and overall survival (OS) in patients with metastatic castration-resistant prostate cancer (mCRPC) and bone metastases treated with radium-223 (Ra-223). Of 101 enrolled patients, 93 were included in the final analysis (median follow-up, 25.2 months; interquartile range, 12.4–31.8). SSEs occurred in 26 patients (28.0%). Median rPFS and OS were 8.8 months (95% CI, 6.1–12.2) and 23.0 months (95% CI, 17.9–27.9), respectively. In multivariable analyses, prostate-specific antigen doubling time (PSADT) ≥ 3 months, estimated glomerular filtration rate ≥ 70 mL/min/1.73 m², and treatment completion (5–6 cycles) were independently associated with a lower risk of SSEs. Treatment completion, PSADT ≥ 3 months, and no prior androgen receptor signaling inhibitor use were independently associated with longer rPFS, whereas treatment completion was independently associated with improved OS. Treatment completion and favorable baseline tumor kinetics, particularly longer PSADT, were associated with better outcomes. Given the potential for selection bias and the exploratory nature of these observational findings, prospective studies are warranted to determine whether initiating Ra-223 during periods of lower disease activity improves outcomes and to clarify the optimal timing of treatment.