Updated interim analysis (IA) of COU-AA-302, a randomized phase III study of abiraterone acetate (AA) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) without prior chemotherapy.

Abstract

5 Background: AA, a specific inhibitor of CYP17, blocks androgen biosynthesis and improves overall survival (OS) in mCRPC post-docetaxel (Lancet Oncol 2012;13:983-92). This pre-specified updated IA (55% total OS events) extends previous IA for COU-AA-302 evaluating clinical benefit of AA vs prednisone (P) in mildly symptomatic or asymptomatic pts with progressive mCRPC without prior chemotherapy. Methods: 1088 pts were stratified by Eastern Cooperative Oncology Group performance status (ECOG-PS, 0 vs 1) and randomized 1:1 to AA 1000 mg + P 5 mg po BID vs Placebo + P. Co-primary endpoints: radiographic progression-free survival (rPFS) and OS. Median time with 95% CI was estimated using the Kaplan-Meier method. The O’Brien-Fleming Lan-DeMets α-spending function was used for OS. Results: At 55% IA, OS, rPFS and secondary endpoints all favored the AA arm (Table). Median follow-up = 27.1 mos. A post hoc sensitivity multivariate analysis for OS using known prognostic factors supported primary results (HR 0.74, P = 0.0017). Grade 3/4 AEs (AA, P) (%): hypertension 4.2 vs 3.1; hypokalemia 2.6 vs 1.9; ALT↑ 5.5 vs 0.7; AST↑ 3.1 vs 0.9. Conclusions: In updated IA of COU-AA-302, improvement in rPFS (risk reduction 47%) remained statistically significant. Risk of death decreased by 21% but did not reach pre-specified efficacy boundary. Median OS for AA (35.3 mos) is the longest reported for this mCRPC population. Secondary endpoints were clinically and statistically significant; safety profile despite longer exposure remains favorable. Targeting extragonadal androgen synthesis reduces morbidity associated with disease progression in mCRPC pts without prior chemotherapy. Clinical trial information: NCT00887198. [Table: see text]