Background
Phase III, double-blind, placebo-controlled RCT. 333 patients with early-stage TNBC (stage II–III). Atezolizumab (PD-L1 inhibitor) added to nab-paclitaxel → anthracycline-based NACT. Co-developed with KEYNOTE-522 (pembrolizumab + paclitaxel-carbo → AC) in the same early TNBC space. PD-L1 assessed via SP142 assay (IC staining).
Interventions and follow up
Arm A: Atezolizumab 840mg q2wk + nab-paclitaxel 125mg/m² weekly × 12 → atezolizumab + doxorubicin/cyclophosphamide × 4
Arm B: Placebo + nab-paclitaxel weekly × 12 → placebo + doxorubicin/cyclophosphamide × 4
Primary endpoint: pCR (ypT0/is ypN0) in ITT and PD-L1-positive subgroup
mFollow up: 20.6 months
Arm B: Placebo + nab-paclitaxel weekly × 12 → placebo + doxorubicin/cyclophosphamide × 4
Primary endpoint: pCR (ypT0/is ypN0) in ITT and PD-L1-positive subgroup
mFollow up: 20.6 months
Results
pCR (ITT): 58% vs 41%, difference +16.5%, P=.0044
pCR (PD-L1+ by SP142): 69% vs 49%, difference +20%
pCR (PD-L1-): 48% vs 34%, difference +14%
pCR (PD-L1+ by SP142): 69% vs 49%, difference +20%
pCR (PD-L1-): 48% vs 34%, difference +14%
Adverse events
Overall: Grade ≥3 AEs 60% vs 57%; no new safety signals beyond known atezolizumab profile.
Immune-related: Any grade 40% vs 21%; grade ≥3 5% vs 1%; hypothyroidism 16% vs 5%.
Dermatologic: Rash 38% vs 23%.
Immune-related: Any grade 40% vs 21%; grade ≥3 5% vs 1%; hypothyroidism 16% vs 5%.
Dermatologic: Rash 38% vs 23%.
Conclusions
Atezolizumab + nab-paclitaxel → AC-based NACT significantly improved pCR in early TNBC (ITT), with greater benefit in PD-L1-positive tumors. IMpassion031 demonstrated that PD-L1 inhibition with a different checkpoint inhibitor (anti-PD-L1 vs anti-PD-1 in KEYNOTE-522) also improves pCR in early TNBC.
Key Limitations
No adjuvant phase — unlike KEYNOTE-522, atezolizumab was not continued post-surgery; pCR improvement without EFS/OS data limits definitive conclusions about survival benefit. EFS/OS data not mature at primary analysis. Smaller N (333 vs 1174 in KEYNOTE-522) limits statistical precision. Nab-paclitaxel (not standard paclitaxel + carboplatin as in KEYNOTE-522) — comparative efficacy across trials is confounded by different backbones. Atezolizumab subsequently failed in the mTNBC setting (IMpassion131 negative); PD-L1 testing by different assays (SP142 vs 22C3) complicates cross-trial comparisons.
Clinical Context
IMpassion031 supported atezolizumab's neoadjuvant pCR benefit in early TNBC, but the drug's failure in IMpassion131 (advanced TNBC with paclitaxel, SP142 assay) limited its regulatory trajectory. KEYNOTE-522 (pembrolizumab) is the approved and preferred immunotherapy regimen in early TNBC based on superior EFS and OS data. Atezolizumab is not approved in the early TNBC neoadjuvant setting in most jurisdictions. IMpassion031 is important for mechanistic understanding and the clinical comparison of PD-1 vs PD-L1 inhibition in TNBC.
References