Radium-223 Use in Clinical Practice and Variables Associated With Completion of Therapy.

Radium-223 has shown clinical efficacy in metastatic castration-resistant prostate cancer. Despite improvement in quality of life and survival, practice patterns and utility of this agent outside the context of clinical trials have not been fully characterized. The primary objective in this study was to evaluate variables associated with completion of 5 to 6 radium-223 doses.We conducted retrospective analyses of patients who received radium-223 (n = 135). Patients were classified into 3 cohorts: 1 to 2, 3 to 4, or 5 to 6 radium-223 doses. We evaluated the association of clinical and laboratory variables with the number of cycles administered (5-6 vs. 1-4 doses).Twenty-five patients (18.5%) received 1 to 2 radium-223 doses, 27 (20.0%) received 3 to 4, and 83 (61.5%) received 5 to 6. The most common reasons for treatment discontinuation included disease progression (61.5%, n = 40), patient preference (15.4%, n = 10), and toxicity (10.8%, n = 7). Factors associated with therapy completion in univariate analysis included previous sipuleucel-T treatment (P = .068), no previous abiraterone or enzalutamide treatment (P = .007), hemoglobin ≥ lower limit of normal (LLN; P = .006), white blood cell count ≥ LLN (P = .045), absolute neutrophil count (ANC) ≥ LLN (P = .049), lower alkaline phosphatase (P = .029), and lower lactate dehydrogenase levels (P = .014). Factors associated with therapy completion in multivariable analysis included previous sipuleucel-T treatment (P = .009), hemoglobin ≥ LLN (P = .037), and ANC ≥ LLN (P = .029).Several clinical parameters are associated with radium-223 therapy completion. In general, these parameters reflect earlier disease stage. These data are hypothesis-generating and prospective testing of the optimal number of radium-223 doses is warranted.