Background
Phase III, double-blind, placebo-controlled RCT. 902 patients with previously untreated locally advanced or metastatic TNBC. Atezolizumab (anti-PD-L1) combined with nab-paclitaxel. PD-L1 expression assessed by Ventana SP142 assay (immune cell staining); PD-L1+ defined as IC ≥1%. First major immunotherapy trial in advanced TNBC.
Interventions and follow up
Arm A: Atezolizumab 840mg q2wk + nab-paclitaxel 100mg/m² days 1, 8, 15 of 28-day cycle
Arm B: Placebo + nab-paclitaxel 100mg/m² days 1, 8, 15 of 28-day cycle
Primary endpoint: PFS and OS tested hierarchically (PD-L1+ then ITT)
mFollow up: 18.0 months (primary); longer for OS update
Arm B: Placebo + nab-paclitaxel 100mg/m² days 1, 8, 15 of 28-day cycle
Primary endpoint: PFS and OS tested hierarchically (PD-L1+ then ITT)
mFollow up: 18.0 months (primary); longer for OS update
Results
PFS (PD-L1+): 7.5 vs 5.0mo, HR 0.62, P<.001
OS (PD-L1+, primary): 25.0 vs 15.5mo, HR 0.62, P=.0012 (prespecified α boundary not met)
PFS (ITT): 7.2 vs 5.5mo, HR 0.80 — not significant
OS (ITT): 21.3 vs 17.6mo, HR 0.86 — not significant
OS (PD-L1+, primary): 25.0 vs 15.5mo, HR 0.62, P=.0012 (prespecified α boundary not met)
PFS (ITT): 7.2 vs 5.5mo, HR 0.80 — not significant
OS (ITT): 21.3 vs 17.6mo, HR 0.86 — not significant
Adverse events
Immune-mediated: Any grade 27.0% vs 5.0% (atezolizumab arm); grade ≥3 hepatotoxicity 2.5%; grade ≥3 pneumonitis 1.1%
Neurologic: Grade ≥3 peripheral neuropathy 8.0% vs 8.1%
Constitutional: Grade ≥3 fatigue 5.0% vs 4.0%
Neurologic: Grade ≥3 peripheral neuropathy 8.0% vs 8.1%
Constitutional: Grade ≥3 fatigue 5.0% vs 4.0%
Conclusions
Atezolizumab + nab-paclitaxel showed significant PFS benefit in PD-L1+ mTNBC and a clinically meaningful but statistically marginal OS benefit (did not cross α boundary at interim). The trial established PD-L1 (SP142/IC) as a predictive biomarker in first-line mTNBC and drove initial FDA approval for this combination.
Key Limitations
Key Limitations: The OS endpoint in PD-L1+ did not formally cross the prespecified α boundary despite an OS HR of 0.62 — FDA used benefit-risk assessment for accelerated approval. The SP142 assay is not interchangeable with 22C3 (used in KEYNOTE-355): SP142 measures immune cell PD-L1 (IC), while 22C3 uses CPS. The negative IMpassion131 trial (atezolizumab + paclitaxel, which enrolled a broader population including taxane-pretreated patients) raised questions about nab-paclitaxel specificity. Atezolizumab's accelerated approval was ultimately withdrawn in the US (2021) after confirmatory failure in IMpassion131, narrowing its indication.
Clinical Context
IMpassion130 was foundational — the first randomized evidence for immunotherapy in mTNBC. However, atezolizumab's US FDA approval for mTNBC was voluntarily withdrawn by Roche/Genentech in 2021 following IMpassion131's failure. Pembrolizumab + chemotherapy (KEYNOTE-355, CPS ≥10) subsequently became the approved and preferred first-line IO regimen in PD-L1-positive mTNBC. IMpassion130 remains important for understanding PD-L1 biology, assay selection, and immunotherapy timing in TNBC. ESMO approval (in PD-L1 IC ≥1%) remains valid in some regions.
References