Abstract P6-10-25: Characterization of the tumor immune microenvironment (TME) in early stage HR-positive HER2-positive breast cancer

Abstract

Abstract Background: In patients (pts) with early stage HER2-positive breast cancer (BC) who are treated with combination neoadjuvant chemotherapy (NAC) and HER2-targeted therapy, recent studies report that increased tumor infiltrating lymphocyte (TIL) density is associated with higher rates of pathologic complete response (pCR) and improved overall survival. However, in the subset of HER2-positive pts who are hormone receptor (HR)-positive, less is known about the relationship between the composition of the tumor immune infiltrate and clinical outcomes. In this study, we sought to characterize the TME of pts with early stage HR+ HER2+ BC using H&E-based TIL scoring and multiplex immunohistochemistry to assess for characteristics associated with achievement of pCR after neoadjuvant therapy. Patients & Methods: We identified 25 pts with HR+ HER2+ early stage BC who were treated with NAC at our institution between 2005 and 2016 for whom pretreatment tissue was available for analysis. Twenty-two pts (88%) received neoadjuvant HER2 antibody therapy along with NAC. Twelve pts (48%) received neoadjuvant pertuzumab in addition to trastuzumab. At the time of surgery, 11 pts achieved pCR and 14 had residual carcinoma (RC). H&E slides from pretreatment biopsy samples were scored for both stromal and intratumoral TILs by a BC pathologist using established guidelines. Additionally, quantitative immunofluorescence (qmIF) was performed on pretreatment biopsy samples for 20 pts (9 with pCR, 11 with RC) using an OPAL antibody panel targeting CD3, CD8, CD68, HLADR, FOXP3, and pancytokeratin. Images were analyzed with the Vectra/inForm software platform (Perkin Elmer) to allow for multiparameter phenotyping. Nearest neighbor analysis to assess median distance between immune cell subtypes and tumor cells was performed using phenoptr software. Results: Per TIL scoring, mean stromal TIL (sTIL) density was 28% in the pCR group and 17% in the RC group (p=0.05). Using a cutoff of ≥10% sTIL density, high sTILs were seen in pretreatment samples in 100% (11/11) of pCR pts and in 57% (8/14) of RC pts (p=0.05). Intraepithelial TIL density was not significantly associated with pCR (p=0.12). Per qmIF analysis, there was a numerical but not statistically significant increase in mean stromal CD3+CD8+ cell density (18% vs 11%) and decrease in stromal CD68+ cell density (10% vs 14%) in the pCR group compared to the RC group. Nearest neighbor analysis revealed that the median distance from tumor cells to CD68+ cells was significantly higher in pts with pCR vs. RC (p=0.02). No significant differences in median distance between CD3+CD8+ cells and tumor or CD3+CD8+ cells and CD68+ cells were detected among the two groups. Conclusions: In a population of early stage HR+ HER2+ breast cancer pts who received neoadjuvant therapy, sTIL density by pathology assessment was associated with increased rates of pCR, supporting the hypothesis that the nature of the TME is biologically significant in the subset of HER2+ pts who are also HR+. qmIF is a useful tool to further characterize the density of specific immune cell subtypes and spatial relationships between cell types in the TME. Further studies in larger cohorts are needed to determine more specific immune biomarkers that predict response to combined chemotherapy and HER2-targeted therapy in pts with HR+ HER2+ BC. Citation Format: Kathleen M. Fenn, Douglas K Marks, Rami Vanguri, Shuobo Boboila, Hua Guo, Hanina Hibshoosh, Kevin Kalinsky, Eileen Connolly. Characterization of the tumor immune microenvironment (TME) in early stage HR-positive HER2-positive breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-10-25.