Background
Phase III, double-blind, placebo-controlled RCT. 1195 patients with mCRPC previously treated with docetaxel, disease progression on or after docetaxel-based chemotherapy. All received ongoing ADT. Abiraterone tested in the post-chemotherapy setting as the first pivotal trial of this agent.
Interventions and follow up
Arm A: Abiraterone acetate 1000mg/day orally + prednisone 5mg twice daily + ongoing ADT
Arm B: Placebo + prednisone 5mg twice daily + ongoing ADT
Primary endpoint: Overall survival (OS)
mFollow up: 12.8 mo (interim, OS crossing boundary); updated at final analysis
Arm B: Placebo + prednisone 5mg twice daily + ongoing ADT
Primary endpoint: Overall survival (OS)
mFollow up: 12.8 mo (interim, OS crossing boundary); updated at final analysis
Results
OS: 14.8 vs 10.9 mo, HR 0.65, P<.001
rPFS: 5.6 vs 3.6 mo, HR 0.67, P<.001
PSA response (≥50% decline): 29.5% vs 5.5%
Objective response rate: 14.4% vs 3.0%
rPFS: 5.6 vs 3.6 mo, HR 0.67, P<.001
PSA response (≥50% decline): 29.5% vs 5.5%
Objective response rate: 14.4% vs 3.0%
Adverse events
Overall: Grade ≥3 AEs 55% vs 54%; treatment discontinuation 19% vs 19%
Mineralocorticoid excess: Fluid retention 31% vs 22% (grade ≥3 2% vs 1%); hypokalemia grade ≥3 4% vs 2%; hypertension grade ≥3 1% vs 1%
Cardiac: Cardiac events 13% vs 11%
Hepatic: ALT/AST elevation grade ≥3 4% vs 1%
Mineralocorticoid excess: Fluid retention 31% vs 22% (grade ≥3 2% vs 1%); hypokalemia grade ≥3 4% vs 2%; hypertension grade ≥3 1% vs 1%
Cardiac: Cardiac events 13% vs 11%
Hepatic: ALT/AST elevation grade ≥3 4% vs 1%
Conclusions
Abiraterone acetate + prednisone significantly prolonged OS by 3.9 months and improved all secondary endpoints in post-docetaxel mCRPC, establishing abiraterone as the first hormonal agent to improve survival in this previously treated population and inaugurating the era of post-chemotherapy ARPI therapy.
Key Limitations
Key Limitations: Median OS of 14.8 months reflects post-docetaxel mCRPC circa 2010 — prior to availability of enzalutamide, cabazitaxel, PARP inhibitors, and Lu-PSMA-617, making the absolute OS numbers less applicable today. The trial was unselected for AR amplification, splice variants, or HRR mutations. Low-dose prednisone was co-administered in both arms, so its independent contribution to OS is not assessable. The 3.9-month median OS gain is modest in absolute terms, though the HR of 0.65 was statistically and clinically significant.
Clinical Context
COU-AA-301 received FDA approval in 2011 for post-docetaxel mCRPC. The companion trial COU-AA-302 extended its use to chemotherapy-naïve mCRPC. Today, abiraterone is predominantly used in earlier disease settings (mHSPC, first-line mCRPC); in the later-line post-ARPI setting, PARP inhibitors, Lu-PSMA-617, and cabazitaxel have largely supplanted repeat ARPI therapy.
References
References: de Bono JS et al, NEJM 2011