Abstract P2-23-05: Trastuzumab-Induced Tumor Microenvironment Changes in Early HER2+ Breast Cancer

Abstract

Abstract Background Trastuzumab (H) is a critical component of therapy (tx) for HER2+ breast cancers (BCs) and can induce anti-tumor immune responses that as part of its mechanism of action. Pre-clinical studies have suggested that antibody-dependent cell-mediated cytotoxicity (ADCC) through NK cells is a major driver of the immune response. However, there is also evidence that macrophages and dendritic cells (DCs) can play an important role in H immune response through antibody-dependent cellular phagocytosis (ADCP). Here, we present pre- and post-tx gene expression and immunohistochemistry (IHC) data to characterize the tumor microenvironment (TME) changes in response to a single dose of H in patients (pts) with early HER2+ BC. Methods Pts with Stage I-III HER2+ BC with minimum 1 cm tumors were eligible. Pts received 8 mg/kg IV H followed by tissue collection. There was a minimum of 14 days between (btw) H and post-tx tissue collection. Pre- and post-tx tissues were assessed for tumor-infiltrating lymphocytes (TILs), immune-related gene expression, and AE1/3, CD31, CD4, CD8, CD11b, CD68, and CD56 expression through IHC. Results Thirteen pts were enrolled and evaluable. 5/13 were estrogen-receptor positive (ER+). TILs were assessed independently by two pathologists and the results averaged. Tx with H resulted in an increase in TILs in the post-tx tissue (p < 0.01). Pre-tx TILs ranged from 2-80% (median 6%) and post-tx TILs ranged from 2-80% (median 20%). 6/13 pts had immune infiltration (Inf), defined as a TIL increase of greater than 1 decile btw pre- and post-tx samples. 2/6 pts with Inf were ER+. Pts with Inf had a significantly higher DC immune signature (ISS) compared to pts without Inf (p < 0.01, univariate analysis). No other ISS reached significance. 6 pts had paired pre- and post-tx samples evaluated by IHC. 4/6 pts had Inf per prior definition. Pts with Inf had an increase in CD11b+ (includes macrophages and some DCs) and CD56+ cells (includes NK cells) after H tx within the tumor compartment (p < 0.05). Pts with Inf had an increase in CD11b+, CD56+, and CD44+ cells in the stromal compartment (p < 0.05). Conclusions Innate immune cells such as macrophages and DCs are key players in H-induced immune response in the early HER2+ BC TME. This data is consistent with prior pre-clinical findings. Citation Format: Laura C. Kennedy, Rebeca Alvarez, Suzanne Dintzis, Vijayakrishna K. Gadi. Trastuzumab-Induced Tumor Microenvironment Changes in Early HER2+ 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 P2-23-05.