A population-based study of the use of radium 223 in metastatic castration-resistant prostate cancer: Factors associated with treatment completion

Abstract

Introduction: Radium 223 (Ra223) given for six cycles has proven efficacy in clinical trials, but its population-level generalizability has not been well-described. The objectives of this study were to describe population-based Ra223 use in the abiraterone and enzalutamide era and identify factors associated with completion. Methods: All Ra223 patients at the British Columbia Cancer Agency between September 2013 and February 2016 were identified. Patients who completed <5 vs. =5 cycles were compared on patient characteristics, lines of prior therapy, prostate-specific antigen (PSA) and alkaline phosphatase (ALP) decline >30% from baseline (R30%), and survival, to identify factors associated with therapy completion. Results: Ninety-one patients were identified; 48 (52.7%) completed >5 cycles. Median overall survival (mOS) was 10.7 months, PSA and ALP R30% were 21% and 52%, respectively. Completion of <5 cycles was associated with higher baseline ALP (p=0.05) and lower baseline hemoglobin (Hb) levels (p=0.03). Patients in the =5 cycles group had longer mOS than those in the <5 cycles group (16.2 vs. 5.9 months; p<0.0001), as well as higher PSA R30% (33.3% vs. 7.0%; p=0.002) and ALP R30% (66.7% vs. 34.9%; p=0.03). Patients with ALP =220 and Hb =118 had 3.85 times the odds of not completing =5 cycles vs. ALP <220 and Hb >118. Conclusions: Compared to clinical trials, patients in a populationbased setting had more lines of therapy and shorter survival. Lower ALP and higher hemoglobin were associated with completion of >5 cycles, longer mOS, and greater incidence of PSA and ALP response.