Abstract P3-01-08: Infiltrating immune cells in the tumor emboli of inflammatory breast cancer

Abstract INTRODUCTION: Inflammatory breast cancer (IBC) is a rare and aggressive type of locally advanced breast cancer. The hallmark of IBC is the presence of E-Cadherin positive tumor emboli within the dermal and parenchymal lymphatic vessels. These tumor emboli are thought to be responsible for the clinical presentation by the physical obstruction of draining lymph vessels. In addition, the intravascular growth of tumor emboli may account for the typical diffuse growth pattern and the fast local spread associated with IBC. Tumor emboli can result from encircling lymphovasculogenesis or lymphovascular invasion and little is known about the infiltrating immune cells in these emboli. This is the first study to investigate the immune infiltrate in the tumor emboli of patients with IBC. METHODOLOGY: To analyze the immune composition of the emboli, four slides of 24 IBC patients were stained according to a validated protocol and scored using the VISIOPHARM® software that makes virtual multiplexing possible after the alignment of different digital slides. We used four validated antibodies: CD79α (B-cell lineage), CD8 (cytotoxic T-cells), FOXP3 (Tregs) and CD163 (Tumor associated macrophages; TAMs), combined with a standard H&E stained section to mark the tumor area and tumor emboli on pretreatment biopsy sections. RESULTS: Half of the IBC patients presented with a hormone receptor positive carcinoma (54.2% - n= 13/24) and 8 out of 21 patients with initially localized disease achieved complete pathological response (pCR) after neo-adjuvant chemotherapy (NACT). Our results are summarized in table 1. Table 1: For every staining we report the number of patients that have infiltrated emboli, the median density in the invasive carcinoma (IC), the median density in the emboli (E) and the ratio between the invasive tumor and emboli in table 1.# patientsDensity (IC) #/μm2Density (E) #/μm2Ratio Density E/ICP-valueCD812/24 (50 %)19.62.40.11< .001CD16319/23 (83 %)35.412.80.43.02CD79α11/24 (46 %)18.23.50.31.01FOXP34/23 (17 %)5.10.30.04.003 Patients with more immune cells in the invasive carcinoma (IC) also had more immune cells in the emboli (E). This correlation was significant for all stainings (Table 1). CD163+ macrophages are the most abundant immune cells in emboli, especially when compared to the invasive carcinoma, whereas CD8+ cells were uncommon in the emboli. The density of CD8+ cells in the invasive carcinoma or emboli did not predict pCR. Interestingly, patients with a higher IC/E CD8 density ratio achieved more often pCR (Kruskal-Wallis χ = 3.6, P = 0.05). Only 20.8% (n= 5/24) had invasive carcinoma directly surrounding the intravascular emboli, however, median overall survival in these patients was significantly shorter (P= 0.003). CONCLUSIONS: This is the first study looking at infiltrating immune cells in IBC. Although based on a small discovery cohort of only 24 patients, we showed that there is a strong correlation between the density of immune cells in the emboli and the density in the invasive carcinoma. Furthermore, we demonstrate that TAMs are the predominant immune cell type in IBC emboli. Cytotoxic T cells are less common and having more CD8+ cells in the invasive carcinoma compared to the emboli was associated with pCR. Patients with invasive carcinoma directly surrounding the emboli had a worse prognosis. Citation Format: Christophe Van Berckelaer, Charlotte Rypens, Peter Vermeulen, Steven Van Laere, Peter Van Dam, Cecile Colpaert. Infiltrating immune cells in the tumor emboli of inflammatory 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 P3-01-08.