Updated Interim Efficacy Analysis and Long-term Safety of Abiraterone Acetate in Metastatic Castration-resistant Prostate Cancer Patients Without Prior Chemotherapy (COU-AA-302)

BackgroundAbiraterone acetate (an androgen biosynthesis inhibitor) plus prednisone is approved for treating patients with metastatic castration-resistant prostate cancer (mCRPC). Study COU-AA-302 evaluated abiraterone acetate plus prednisone versus prednisone alone in mildly symptomatic or asymptomatic patients with progressive mCRPC without prior chemotherapy.ObjectiveReport the prespecified third interim analysis (IA) of efficacy and safety outcomes in study COU-AA-302.Design, setting, and participantsStudy COU-AA-302, a double-blind placebo-controlled study, enrolled patients with mCRPC from April 2009 to June 2010. A total of 1088 patients were stratified by Eastern Cooperative Oncology Group performance status (0 vs 1).InterventionPatients were randomised 1:1 to abiraterone 1000mg plus prednisone 5mg twice daily by mouth versus prednisone.Outcome measurements and statistical analysisCo-primary end points were radiographic progression-free survival (rPFS) and overall survival (OS). Median times to event outcomes were estimated using the Kaplan-Meier method. Hazard ratios (HRs) and 95% confidence intervals (CIs) were derived using the Cox model, and treatment comparison used the log-rank test. The O'Brien-Fleming Lan-DeMets α-spending function was used for OS. Adverse events were summarised descriptively.Results and limitationsWith a median follow-up duration of 27.1 mo, improvement in rPFS was statistically significant with abiraterone treatment versus prednisone (median: 16.5 vs 8.2 mo; HR: 0.52 [95% CI, 0.45-0.61]; p2 yr.