Factors Associated With Survival Following Radium-223 Treatment for Metastatic Castration-resistant Prostate Cancer

Background: Radium-223 (²²³Ra) improves survival in patients with metastatic castration-resistant prostate cancer (mCRPC). This retrospective analysis was performed to better understand its efficacy in routine clinical practice and identify factors associated with survival. Materials and Methods: Sixty-four patients with mCRPC who received ²²³Ra between 2013 and 2015 were the basis of this retrospective study. Clinical outcomes and patient characteristics were obtained. Potential prognostic factors for survival were evaluated by univariate analysis using the log-rank test and multivariate analysis using the Cox proportional hazard method. Results: The median survival was 12.9 months. Twenty-one patients (33%) developed a skeletal event, and the median time to the first skeletal event was 4.4 months. In univariate analysis, factors significantly associated with survival included: no prior chemotherapy, ≤ 5 bone metastases, baseline prostate-specific antigen (PSA) ≤ 36 ng/mL, baseline alkaline phosphatase (ALP) < 115 U/L, baseline hemoglobin > 12 g/dL, ALP response after ²²³Ra treatment, PSA decrease during ²²³Ra treatment, and absence of > 25% PSA increase during ²²³Ra treatment. In multivariate analysis, 4 factors remained significant: no prior chemotherapy, ≤ 5 bone metastases, baseline ALP < 115 U/L, and ALP response after ²²³Ra treatment. Conclusion: When ²²³Ra is administered in routine clinical practice, clinical outcomes can be more variable than those reported in the randomized study owing to patient heterogeneity. Four factors were identified to be significantly associated with survival after ²²³Ra treatment. These pretreatment factors may be used as stratification factors in future studies to investigate whether ²²³Ra would be more effective for patients with newly diagnosed metastatic disease that is sensitive to androgen deprivation therapy.