Abstract OT1-01-01: IMpassion131: A phase III study comparing 1L atezolizumab with paclitaxel vs placebo with paclitaxel in treatment-naive patients with inoperable locally advanced or metastatic triple negative breast cancer (TNBC)

Background: Chemotherapy (including paclitaxel) remains the predominant treatment for metastatic TNBC but clinical outcomes remain poor. Therefore, new therapeutic approaches are needed. Atezolizumab blocks the binding of PD-L1 to its receptors PD-1 and B7.1, thus restoring tumor-specific T cell immunity. TNBC is a rational target for atezolizumab therapy due to high PD-L1 expression on tumor-infiltrating immune cells (IC) and elevated T cell tumor infiltration. Furthermore, combining chemotherapy with atezolizumab is hypothesized to enhance anti-tumor immune response via neoantigen release. Atezolizumab alone and in combination with nab-paclitaxel has demonstrated promising clinical benefit in metastatic TNBC and was well tolerated, with no exacerbation of chemotherapy-associated adverse events. Atezolizumab in combination with nab-paclitaxel is being further investigated as 1L TNBC treatment in IMpassion130. IMpassion131 is a global, multi-center, randomized, double-blind, placebo-controlled study comparing the efficacy and safety of 1L atezolizumab + paclitaxel vs placebo + paclitaxel in patients with untreated, inoperable, locally advanced or metastatic TNBC. (NCT03125902) Methods: Eligibility criteria include patients with inoperable, locally advanced or metastatic TNBC, histologically confirmed; de novo or recurrent disease after early breast cancer treated with chemotherapy ≥ 12 months prior; eligible for taxane monotherapy; no prior chemotherapy or targeted systemic therapy for inoperable locally advanced or metastatic disease; ECOG PS 0-1 and measurable disease by RECIST v1.1. Exclusion criteria include known symptomatic CNS disease, prior immunotherapy and a history of autoimmune disease. Approximately 495 patients will be randomized 2:1 to receive atezolizumab (840 mg) or placebo (q2w; days 1 and 15 of 28-day cycle) plus paclitaxel (90 mg/m 2 ; days 1, 8, 15 of 28-day cycle) until disease progression. Stratification factors are PD-L1 expression on tumor-infiltrating IC (IC0 Citation Format: Miles D, Andre F, Gligorov J, Verma S, Xu B, Cameron D, Barrios CH, Schneeweiss A, Easton V, Ghazi Y, O9Shaughnessy J. IMpassion131: A phase III study comparing 1L atezolizumab with paclitaxel vs placebo with paclitaxel in treatment-naive patients with inoperable locally advanced or metastatic triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT1-01-01.