Assessment of Real-World Central Nervous System Events in Patients with Advanced Prostate Cancer Using Abiraterone Acetate, Bicalutamide, Enzalutamide, or Chemotherapy.

BACKGROUND Central nervous system (CNS) events are frequently reported among patients with advanced prostate cancer as a consequence of the treatments used in this patient population. OBJECTIVE To assess the incidence of CNS events in patients with advanced prostate cancer who initiated treatment with abiraterone acetate, bicalutamide, enzalutamide, or chemotherapy. METHODS The Truven Health MarketScan Research databases were used to retrospectively identify patients with prostate cancer who initiated treatment with abiraterone acetate, enzalutamide, bicalutamide, or chemotherapy after September 1, 2012 (ie, the index date). The chemotherapy agents included cabazitaxel, docetaxel, mitoxantrone hydrochloride, and estramustine, and were used as monotherapy or as combination therapy. Patients were followed until December 31, 2014, the end of exposure to treatment, or until loss to follow-up. Kaplan-Meier rates and adjusted Cox proportional hazard models were used to compare the incidence of CNS events between the abiraterone acetate cohort and the other cohorts. A sensitivity analysis of patients with a diagnosis of metastasis was also conducted. RESULTS A total of 1067 patients receiving abiraterone acetate, 5524 receiving bicalutamide, 592 receiving enzalutamide, and 256 receiving chemotherapy were identified. After 12 months, patients who received abiraterone acetate were less likely to have a CNS event than patients who received enzalutamide (39.5% vs 46.0%, respectively; P = .0036) or chemotherapy (39.5% vs 51.1%, respectively; P = .0277), and were more likely to have a CNS event than patients who received bicalutamide (39.5% vs 34.2%, respectively; P = .0397). After multivariate adjustment, at 12 months, patients who initiated abiraterone acetate treatment had 20% (P = .0388) reduction in the risk for a CNS event compared with patients who initiated enzalutamide; 8% (P = .3622) versus bicalutamide; and 27% (P = .0456) versus chemotherapy. The sensitivity analysis yielded similar results. CONCLUSION The results of this large observational study suggest that among patients with metastatic prostate cancer, treatment with abiraterone acetate is associated with a significantly lower likelihood of having a CNS event compared with treatment with enzalutamide or chemotherapy, but not with bicalutamide, even when controlling for metastatic disease.