Abstract P4-08-19: Biomarker analysis: Multi-omics elucidation of Cohort 1 from a phase II study of a triple combination of Atezolizumab + cobimetinib + eribulin in patients with metastatic inflammatory breast cancer

Abstract Background: Inflammatory breast cancer (IBC) is a rare but aggressive tumor type accounting for up to 10% of breast cancer deaths. One-third of IBCs express high PD-L1 that can be targeted by atezolizumab (Az). MEK inhibitor cobimetinib (Co) not only inhibits the RAS-MAPK pathway but can further enhance immune-mediated killing. Thus, we hypothesize that Az+Co may enhance the efficacy of chemotherapy in metastatic IBC (mIBC). We opened a trial to test this hypothesis with a comprehensive multi-omics biomarker assessment. Patients and Methods: In a single-center, open-label phase II study, cohort 1 received one cycle of Az+ Co, followed by four cycles of Az+Co+eribulin (E) to induce a maximum clinical response, followed by Az+Co maintenance. Pre and Post one cycle of Az+Co tumors were collected for immunohistochemistry (IHC), multiplex immunofluorescence (mIF), whole-exome sequencing (WES), and RNA sequencing (RNAseq). Blood was collected for circulating tumor DNA (ctDNA). Results: Seventeen patients were enrolled in cohort 1. Seven had PR, and three had SD as the best responses. Fourteen had pre, and six had pre/post tumors. The levels of PD-L1 expression at pre/post were not associated with responses. WES revealed the median tumor mutation burden at pre- was 9mt/Mb. More than 50% had TP53 and PI3K pathway mutations at pre. RTK-RAS and Notch pathways were altered in 4/9 cases. PRDM9 and DPY19L2 single-gene mutations were commonly noted in pre. No cancer-associated gene aberration, including potential biomarkers of anti-PDL1 agent response was associated with clinical outcomes. Transcriptomic gene set enrichment analysis demonstrated a greater degree of TNFa and TGFb signaling, Oxphos, angiogenesis, and epithelial-to-mesenchymal transition (EMT) processes in tumors from patients with poor response. Immune profiling by RNAseq revealed two responders to have elevated effector memory T cells, NK T cells, myeloid dendritic cells, and M1 macrophage signatures in pre-samples, but post-samples were not available. mIF confirmed a higher frequency of NK-T cells. The ctDNA analysis from serially collected blood samples is ongoing. Discussion: In this comprehensive multi-omics analysis of pre-and-post-Az+Co, we observed several novel findings, while conventional biomarkers for Az and Co did not correlate with clinical responses. EMT, Oxphos, Notch, and chronic inflammation pathways, which are not previously well reported, were observed in this IBC cohort. These markers warrant further validation to see if they carry significance as therapeutic targets in IBC. Citation Format: Bora Lim, Angela Alexander, Jie S. Willey, Huiming Sun, Suyu Liu, Anisha B. Patel, Edwin Roger Parra, Cara Haymaker, Luisa Solis Soto, Alejandra Serrano, Baohua Sun, Cibelle Freitas Pinto Lima, Auriole Tamegnon, Renganayaki K. Pandurengan, Dzifa Douse, Jessica Lan, Luthra Raja, Randy Chu, Mark Knafl, Scott E. Woodman, Haifeng Zhu, Katja Shulze, Katherine Fedenko, Walter Darbonne, Naoto T. Ueno, Vicente Valero. Biomarker analysis: Multi-omics elucidation of Cohort 1 from a phase II study of a triple combination of Atezolizumab + cobimetinib + eribulin in patients with metastatic inflammatory breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-08-19.