Background
Phase III, double-blind, placebo-controlled RCT. 1088 patients with asymptomatic or mildly symptomatic chemotherapy-naïve mCRPC, ongoing ADT, ECOG PS 0–1, no prior docetaxel. Examined whether abiraterone is effective before chemotherapy in mCRPC, building on COU-AA-301 data in the post-docetaxel setting.
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: Radiographic PFS (rPFS) and OS (co-primary, tested hierarchically)
mFollow up: 22.2 mo (rPFS analysis); 49.2 mo (final OS)
Arm B: Placebo + prednisone 5mg twice daily + ongoing ADT
Primary endpoint: Radiographic PFS (rPFS) and OS (co-primary, tested hierarchically)
mFollow up: 22.2 mo (rPFS analysis); 49.2 mo (final OS)
Results
rPFS: 16.5 vs 8.3 mo, HR 0.53, P<.001
OS: 34.7 vs 30.3 mo, HR 0.81, P=.0033
Time to chemotherapy: 25.2 vs 16.8 mo, HR 0.58
PSA response (≥50% decline): 62% vs 24%
OS: 34.7 vs 30.3 mo, HR 0.81, P=.0033
Time to chemotherapy: 25.2 vs 16.8 mo, HR 0.58
PSA response (≥50% decline): 62% vs 24%
Adverse events
Overall: Grade ≥3 AEs 48% vs 42%; discontinuation due to AEs 24% vs 19%
Mineralocorticoid excess: Fluid retention 28% vs 24%; hypertension grade ≥3 4% vs 3%; hypokalemia grade ≥3 2% vs 1%
Cardiac: Grade ≥3 5% vs 3%
Hepatic: Grade ≥3 6% vs 1%
Constitutional: Fatigue grade ≥3 8% vs 5%
Mineralocorticoid excess: Fluid retention 28% vs 24%; hypertension grade ≥3 4% vs 3%; hypokalemia grade ≥3 2% vs 1%
Cardiac: Grade ≥3 5% vs 3%
Hepatic: Grade ≥3 6% vs 1%
Constitutional: Fatigue grade ≥3 8% vs 5%
Conclusions
Abiraterone acetate significantly prolonged rPFS and OS in chemotherapy-naïve mCRPC, establishing abiraterone as an effective pre-chemotherapy option and extending the survival benefit seen in COU-AA-301 to earlier-stage mCRPC.
Key Limitations
Key Limitations: OS benefit was modest in absolute terms (4.4 months), and the OS co-primary endpoint barely crossed the pre-specified boundary. Liver function test elevations necessitate monitoring. The trial enrolled asymptomatic/mildly symptomatic patients — applicability to symptomatic mCRPC is less clear. In the modern treatment landscape, many patients reaching mCRPC have already received abiraterone or enzalutamide in the mHSPC setting, making first-line mCRPC ARPI-naïve patients a minority.
Clinical Context
COU-AA-302 received FDA approval in 2012 for chemotherapy-naïve mCRPC, complementing COU-AA-301. Abiraterone is now mostly used in mHSPC (post-LATITUDE and STAMPEDE-abi). The mCRPC first-line landscape has shifted: most patients reaching mCRPC today will have had prior ARPI in the mHSPC setting, and first-line mCRPC options now include PARP inhibitors (for HRR-mutated disease) and Lu-PSMA-617 (PSMAfore, post-ARPI taxane-naïve).
References
References: Ryan CJ et al, NEJM 2013