Background
Phase III double-blind RCT (IMpower133); N=403; systemic-therapy-naïve extensive-stage SCLC; 1:1 randomization, stratified by sex, ECOG PS, brain metastases.
Interventions and follow up
Arm A: Atezolizumab 1200mg + carboplatin AUC5 D1 + etoposide 100mg/m2 D1-3 Q21 x4, then maintenance atezolizumab until progression/toxicity
Arm B: Placebo + carboplatin/etoposide x4, then maintenance placebo
Primary endpoints: Overall survival and investigator-assessed PFS
mFollow up: 13.9 mo
Arm B: Placebo + carboplatin/etoposide x4, then maintenance placebo
Primary endpoints: Overall survival and investigator-assessed PFS
mFollow up: 13.9 mo
Results
mOS: 12.3mo vs 10.3mo (A vs B), HR 0.70, 95% CI 0.54-0.91, P=.007
mPFS: 5.2mo vs 4.3mo, HR 0.77, 95% CI 0.62-0.96, P=.02
1-yr OS: 51.7% vs 38.2%
mPFS: 5.2mo vs 4.3mo, HR 0.77, 95% CI 0.62-0.96, P=.02
1-yr OS: 51.7% vs 38.2%
Adverse events
Overall: Grade 3-4 events 56.6% vs 56.1% (A vs B)
Hematologic: Neutropenia, anemia, decreased neutrophil count most common grade 3-4
Immune-related: Any-grade irAE 39.9% vs 24.5%
Hematologic: Neutropenia, anemia, decreased neutrophil count most common grade 3-4
Immune-related: Any-grade irAE 39.9% vs 24.5%
Conclusions
Adding atezolizumab to carboplatin/etoposide significantly improved OS and PFS in first-line extensive-stage SCLC, establishing chemoimmunotherapy as a new standard of care.
Key Limitations
Modest absolute OS gain (~2mo); no validated predictive biomarker (benefit independent of PD-L1/bTMB); patients with treated asymptomatic CNS mets eligible but untreated CNS excluded.
Clinical Context
FDA approved atezolizumab + carboplatin/etoposide for first-line ES-SCLC (Mar 2019); EMA approved 2019. ESMO endorses chemoimmunotherapy as first-line standard. Parallel data with durvalumab (CASPIAN).
References