Integration of radium-223 dichloride (Xofigo) into clinical practice for the treatment of castration-resistant prostate cancer.

Abstract

312 Background: Radium-223 dichloride (Xofigo) is an FDA-approved radionuclide used to treat symptomatic bone metastases in patients with castration-resistant prostate cancer (CRPC) with no known visceral metastases. Outside of clinical trial, the benefits of Radium-223 dichloride (Ra-223) in the treatment of CRPC have not yet been fully delineated in real life setting. Therefore, the purpose of this study was to evaluate the outcome of patients with CRPC who were treated with Ra-223, especially studying the variables associated with completion of 6 cycles of therapy. Methods: A total of 114 patients with CRPC and bone metastases referred for treatment with Ra-223 between March 2010 and February 2018 were identified for retrospective analysis. A chart review was conducted to analyze clinical characteristics, treatments, and outcomes including radiologic bone scans. Categorical variables were compared using Chi-square and independent student t test, and survival rates were generated using Kaplan-Meier analysis. Multivariate analysis (MVA) Cox proportional hazard ratios (HR) model was used in the assessment of OS and PFS. Results: Of the 114 patients referred for treatment, the overall median OS was 12.6 months. In MVA, improved OS was most strongly associated with completion of all six doses (p < 0.001). Median OS for the 56 patients who received full treatment was 24 months, while median OS for the 107 patients who did not complete treatment was 5.9 months. In univariate analysis, treatment completion was significantly associated with prior Sipuleucel-T (p = 0.002), concurrent Denosumab (p = 0.027), and baseline PSA < 30 ng/mL (p = 0.004). Conclusions: Completion of treatment with Ra-223 is a significant factor associated with improved OS. Therefore it is clinically important to delineate which patients are to the most appropriate candidates to complete treatment. Factors notable for treatment completion suggest patients might benefit from initiating Ra-223 treatment after receiving Sipuleucel-T and while their PSA remains low. Further consideration should be given to the sequence of Ra-223 in clinical practice, including use of concurrent Abiraterone and Enzalutamide.