Abstract GS1-04: IMpassion130: Efficacy in immune biomarker subgroups from the global, randomized, double-blind, placebo-controlled, phase III study of atezolizumab +nab-paclitaxel in patients with treatment-naïve, locally advanced or metastatic triple-negative breast cancer

Background: The Phase III IMpassion130 study (NCT02425891) evaluated atezolizumab (anti–PD-L1) + nab -paclitaxel (nabPx) vs placebo + nabPx as first-line treatment for pts with metastatic triple-negative breast cancer (TNBC). The study met its co-primary PFS endpoint in ITT pts and in pts with PD-L1 ≥1% on tumor-infiltrating immune cells (IC+). Clinically meaningful OS benefit was seen at interim OS analysis, notably in pts with PD-L1 IC+ tumors (Table). Here we report exploratory efficacy data in immunologically and clinically relevant, biomarker-defined subgroups. Methods: Pts had histologically documented metastatic or unresectable locally advanced TNBC (evaluated locally per ASCO-CAP). Pts were randomized 1:1 to nabPx 100 mg/m 2 IV (d1, 8 and 15 of a 28-d cycle) + atezolizumab 840 mg IV q2w or placebo (A-nabPx or P-nabPx) until progression or toxicity. Exploratory biomarkers were centrally analyzed: PD-L1 on tumor cells (TC) by VENTANA SP142 IHC assay, intratumoral CD8 by IHC, stromal tumor-infiltrating lymphocytes (sTILs), BRCA1/2 mutational status and ER/PR/HER2 status. Results: PD-L1 IC was highly predictive of A-nabPx efficacy (Table). The majority of PD-L1 TC+ tumors were also PD-L1 IC+. Intratumoral CD8, but not sTILs, were well correlated with PD-L1 IC. Consequently, CD8 was predictive of A-nabPx efficacy for PFS/OS, while sTILs only predicted PFS benefit. Local vs central TNBC assessment was concordant in most pts. Local vs central lab–defined TNBC populations derived similar benefit from A-nabPx. Efficacy by BRCA status will be presented to evaluate the benefits of immunotherapy for this subgroup. Conclusions: Exploratory efficacy analyses from IMpassion130 suggest consistency between local and central ER/PR/HER2 testing and that PD-L1 IC is the most robust predictive biomarker for selecting untreated mTNBC pts who benefit from A-nabPx. Citation Format: Emens LA, Loi S, Rugo HS, Schneeweiss A, Dieras V, Iwata H, Barrios CH, Nechaeva M, Molinero L, Nguyen Duc A, Funke R, Chui SY, Husain A, Winer EP, Adams S, Schmid P. IMpassion130: Efficacy in immune biomarker subgroups from the global, randomized, double-blind, placebo-controlled, phase III study of atezolizumab + nab -paclitaxel in patients with treatment-naive, locally advanced or metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS1-04.