Value of bone scan index for predicting overall survival among patients treated with radium-223 for bone metastatic castration-resistant prostate cancer.

Abstract

216 Background: The objective of this study was to evaluate the bone scan index (BSI) as a prognostic biomarker for overall survival (OS) among patients treated with radium-223 (Ra-223) for bone metastatic castration-resistant prostate cancer (mCRPC). Methods: We retrospectively identified 42 men who had been treated with Ra-223 for bone metastatic CRPC between 2012 and 2017 and investigated correlations between the baseline clinical factors of age, time to CRPC, previous use of docetaxel, PSA, Gleason score, alkaline phosphatase (ALP), and BSI and OS by multivariate analysis using the Cox proportional hazard model. We also analyzed the correlations between OS and absolute BSI value or BSI change from baseline after 12 weeks of treatment. Continuous variables were classified as dichotomous. Results: The median age, PSA, and time to CRPC were 75.5 years, 42.8 ng/mL, and 11.2 months, respectively. The median observation period was 11.7 months. Twenty-five (59.5 %) of the 42 patients had completed six cycles of Ra-223 treatment. Twenty-two patients (52.4 %) had died, including 20 (47.6 %) of cancer, by the time of analysis. The median OS in the entire cohort was 20.7 months. Multivariate analysis also showed that only BSI (≥1.5 vs. < 1.5, HR 3.72, 95% CI 1.17–11.79, p = 0.026) was significantly correlated with OS. The BSI had decreased in 16 (51.6%) of the 31 patients who had undergone bone scans after 12 weeks of treatment . Multivariate analysis showed that absolute BSI value after 12 weeks treatment was significantly correlated with OS (BSI (≥2.0 vs. < 2.0%, HR 13.07, 95% CI 2.61–65.53, p = 0.002). No correlation was found between BSI change from baseline after 12 weeks and OS. Conclusions: According to multivariate analysis, both baseline BSI and PSA were significant prognostic factors for OS among men treated with Ra-223. Absolute BSI value after 12 weeks of Ra-223 treatment was also found to be an independent prognostic factor for OS.