Abstract HER2-01: HER2-01 Clinical and Molecular Characteristics of HER2-low/zero Early Stage Triple-Negative Breast Cancer
Authors: Yam Clinton , Li Ziyi , Korkut Anil , Ma Wencai , Kong Elisabeth , Hill Holly A. , Abbas Hussein , Abouharb Sausan , Adrada Beatriz , Arun Banu K. , Barcenas Carlos H. , Bisen Ajit , Booser Daniel , Buzdar Aman , Candelaria Rosalind , Chen Junjie , Clayborn Alyson , Damodaran Senthil , Ding Qingqing , Garber Haven , Hortobagyi Gabriel N. , Hunt Kelly K. , Ibrahim Nuhad K. , Iheme Adaeze , Karuturi Meghan S. , Koenig Kimberly , Layman Rachel M. , Lee Jangsoon , Litton Jennifer K. , Mitchell Melissa , Moscol Giancarlo , Mouabbi Jason , Murthy Rashmi K. , Oke Oluchi , Pohlmann Paula , Ramirez David , Ravenberg Elizabeth , Saleem Sadia , Teshome Mediget , Valero Vicente , White Jason , Williams Madison , Woodward Wendy , Yajima Chasity , Ueno Naoto T. , Chen Ken , Rauch Gaiane , Huo Lei , Tripathy Debu 
Published: March 2023

Background: In the metastatic setting, low HER2 expression is associated with clinical benefit from trastuzumab deruxtecan, a HER2-targeting antibody drug conjugates. However, little is known about the biological significance of low HER2 expression in patients with early stage triple-negative breast cancer (TNBC) receiving neoadjuvant therapy (NAT). Methods: Out of 595 patients with stage I-III TNBC enrolled on the prospective ARTEMIS trial (NCT02276443) from 2015-2021, we identified 367 patients with available HER2 immunohistochemistry (IHC) results on pre-NAT tumor tissue (HER2-zero: n=218; HER2-low [IHC 1+, 2+]: n=149). All patients were treated with anthracycline-based NAT. In cases where sufficient pre-NAT tumor tissue were available, additional IHC and/or RNAseq were performed. Differential gene expression (DGE) and pathway analysis were performed using DEseq2. Gene set enrichment analysis (GSEA) was performed using the Hallmark gene sets. Deconvolution analyses were performed using CIBERSORT. We controlled for multiple hypothesis using a false discovery rate (FDR) threshold with the Benjamini-Hochberg method, accepting as significant genes with at least a 2-fold change and &lt; 5% FDR. Results: Table 1 summarizes baseline clinicopathological features of the 367 patients. Compared to HER2-zero tumors, HER2-low tumors were less likely of metaplastic histology (p=0.001), associated with lower Ki67 (p=0.017) and were more likely to be androgen receptor (AR)-positive (p=0.01). There were no significant differences in tumor-infiltrating lymphocytes (TILs) infiltration and PD-L1 expression between HER2-zero and HER2-low tumors. Among the 226 patients with sufficient pre-NAT tissue for RNAseq, DGE analyses demonstrated upregulation of genes involved in fatty acid metabolism (ACSM1) and steroid hormone metabolism (DHRS2, UGT2B28) in HER2-low tumors compared with HER2-zero tumors. Deconvolution analyses revealed no significant differences between predicted proportions of immune cell subpopulations between HER2-low and HER2-zero tumors. Although rates of pCR were not significantly different between patients with HER2-zero (46%) and HER2-low tumors (40%) (p=0.34), non-pCR in patients with HER2-low tumors was associated with increased expression of EREG, which encodes an EGFR ligand, while non-pCR in patients with HER2-zero tumors was associated with downregulation in genes involved in immune response pathways. GSEA further identified the Hallmark allograft rejection (FDR q=0.001), interferon gamma response (FDR q=0.002), and interferon alpha response pathways (FDR q=0.007) as the 3 most significantly downregulated pathways in HER2-zero tumors from patients experiencing a non-pCR relative to HER2-zero tumors from patients experiencing a pCR. Conclusion: In early stage TNBC, low HER2 expression is associated with increased AR expression and upregulation of genes associated with fatty acid and steroid hormone metabolism. Gene expression analyses suggest that drivers of resistance to NAT differ between HER2-low and HER2-zero tumors. Biological differences between HER2-zero and HER2-low tumors exist and may influence future personalized treatment for patients with early stage TNBC.

Citation Format: Clinton Yam, Ziyi Li, Anil Korkut, Wencai Ma, Elisabeth Kong, Holly A. Hill, Hussein Abbas, Sausan Abouharb, Beatriz Adrada, Banu K. Arun, Carlos H. Barcenas, Ajit Bisen, Daniel Booser, Aman Buzdar, Rosalind Candelaria, Junjie Chen, Alyson Clayborn, Senthil Damodaran, Qingqing Ding, Haven Garber, Gabriel N. Hortobagyi, Kelly K. Hunt, Nuhad K. Ibrahim, Adaeze Iheme, Meghan S. Karuturi, Kimberly Koenig, Rachel M. Layman, Jangsoon Lee, Jennifer K. Litton, Melissa Mitchell, Giancarlo Moscol, Jason Mouabbi, Rashmi K. Murthy, Oluchi Oke, Paula Pohlmann, David Ramirez, Elizabeth Ravenberg, Sadia Saleem, Mediget Teshome, Vicente Valero, Jason White, Madison Williams, Wendy Woodward, Chasity Yajima, Naoto T. Ueno, Ken Chen, Gaiane Rauch, Lei Huo, Debu Tripathy. HER2-01 Clinical and Molecular Characteristics of HER2-low/zero Early Stage Triple-Negative 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 HER2-01.