One-Year, Open-Label Extension Study on the Safety and Efficacy of Abiraterone Acetate Fine Particle Formulation in Patients With Metastatic Castration-Resistant Prostate Cancer

Abstract

Purpose: Abiraterone acetate is an androgen synthesis inhibitor used to treat metastatic castration-resistant prostate cancer. The therapeutic equivalence, pharmacokinetics, and safety of abiraterone acetate fine particle (AAFP) versus originator abiraterone acetate (OAA) were examined in a Phase-2 study; sufficient similarity was observed between the 2 treatments. This 1-year, open-label, extension study evaluated the long-term safety and efficacy of AAFP. Patients and methods: This was an open-label, single-arm extension study. Patients who completed the 84-day, Phase-2, run-in study could enroll to receive 500 mg AAFP once daily and 4 mg methylprednisolone twice daily for up to 1 year. Safety was the primary endpoint, as assessed by adverse event monitoring throughout the study. Secondary efficacy endpoints included change from run-in study baseline levels of serum testosterone and prostate-specific antigen measured at baseline, 6 months, and 1 year. Results: Twenty patients enrolled, of whom 9 and 11 received prior AAFP and OAA in the run-in study, respectively. Both prior treatment groups maintained a significant decrease in serum testosterone from run-in baseline at all timepoints; mean change from run-in baseline ± standard deviation at 1 year of −6.24 ± 2.02 ( P = .0023) and −5.87 ± 3.64 ( P = .0026) ng/dL for the prior AAFP and OAA group, respectively. Change from run-in baseline in serum prostate-specific antigen was not significant. Most (84.0%) adverse events were Grade 1 or 2. Conclusion: No new safety signals were identified, and patients were able to successfully switch from OAA to AAFP with no impact.