Survival and fracture risk with radium-223 therapy in metastatic castrate-resistant prostate cancer (mCRPC): A real-world analysis.

Abstract

50 Background: Radium-223 is a life-prolonging radionuclide therapy for men with bone-predominant metastatic castrate-resistant prostate cancer (mCRPC). It accumulates at sites of high bone turnover with emerging evidence suggesting use of radium-223 increases risk of pathologic fractures. Bone-protective agents (BPAs) reduce skeletal-related events including pathologic fractures in men with mCRPC. We evaluated real-world outcomes of patients treated with radium-223, including the effect of BPA use on pathologic fracture risk. Methods: This was a single institution retrospective cohort study that included patients with mCRPC treated with radium-223 in Manitoba, Canada from 2014 to 2021. Outcomes of interest included incidence of pathologic fracture, pain response, alkaline phosphatase (ALP) response, and overall survival. Kaplan-Meier method was used for time to event outcomes and multivariable Cox regression models were used to adjust for covariates. Results: We identified 92 patients who received radium-223 for mCRPC (Table). Thirty patients (33%) completed 6 cycles of radium-223. Documented pain relief occurred in 39% of patients. For those with elevated ALP at baseline (n = 46), 57% had at least 30% reduction in total ALP. PSA reduction occurred in 29% with 11% having at least 30% reduction in PSA. Median overall survival (OS) was 9.4 months (95% CI 5.8 to 15.9). Of those who did not receive concurrent BPA, 26% developed a pathologic fracture, compared to 3% who received concurrent BPA during a median follow up of 8.1 months. BPA use was associated with significant delay in time to pathologic fracture (median not reached vs. 15.9 months; HR = 0.20, 95% CI: 0.05 – 0.76, p < 0.05) after adjusting for number of bone metastases and corticosteroid use. Conclusions: In this real-world study, concurrent BPA use was associated with significant reduction in risk of pathologic fractures in mCRPC patients receiving radium-223. BPA administration should be considered for patients receiving radium-223. [Table: see text]