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

Micro-Abstract The outcomes of 64 patients with metastatic castration-resistant prostate cancer after treatment with radium-223 were analyzed. Four factors were identified to be associated with survival in multivariate analysis. Future studies to evaluate earlier use of this radiopharmaceutical in newly diagnosed metastatic prostate cancer when the disease is sensitive to androgen deprivation therapy would be warranted. 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.