Abstract B025: Primary and metastatic tumors from triple negative breast cancer possess distinct immunological profiles
Authors: Goudreau Alexandra D. , Penoit Alexandre , Lasiste Jade Marie , Aleynikova Olga , Katergi Khaled , Lafleur Josiane , Aguilar-Mahecha Adriana , Basik Mark 
Published: November 2024

Abstract
Metastatic triple negative breast cancer (mTNBC) is almost always fatal due to progressive chemoresistance and a lack of therapeutic targets. Stromal cells, including tumor-infiltrating lymphocytes (TILs) and cancer associated fibroblasts (CAFs), are linked to differences in prognosis and therapy response. While evidence in primary TNBC demonstrates how TIL characteristics may influence outcomes and treatment efficacy, studies in the metastatic setting are lacking. Here, we aimed to characterize TIL phenotype and localization relative to CAFs and cancer cells between primary and metastatic tumors in mTNBC, and to correlate these features with clinical outcomes. CAF cellularity was assessed in H&E stained sections of 15 primary and 40 metastatic lesions, including brain (n=4), liver (n=5), lymph node (n=3), chest wall (n=4), as well as local (n=12) and distant cutaneous (n=12) metastases. Based on the surface area covered by fibroblasts, CAF cellularity was designated as low (0-33%) or high (34-100%). Immunohistochemical staining (IHC) was performed to identify cytotoxic (CD8+) and regulatory T cells (FOXP3+). Percentages of CD8+ and FOXP3+ cells were quantified with QuPath, and infiltration patterns were assessed by pathologists. Results were correlated with overall survival (OS) and response to treatment after biopsy, which was defined according to RECIST criteria. As expected, metastases had less CD8+ (p=0.02) and FOXP3+ (p=0.007) cells than primary tumors. While CD8+ cells strongly correlated between primary and metastatic tumors (r=0.71, p=0.03), increased FOXP3+ cells in metastases were associated with high CAF regions (p=0.02). CD8+ cells alone were not prognostic; however, infiltration into the epithelium of metastases significantly improved OS (p=0.02). There was a strong correlation between CD8+ and FOXP3+ cell proportions in metastases (r=0.68, p&lt;0.0001) not seen in primary tumors. CD8:FOXP3+ cell ratios in metastases correlated with longer OS (r=0.51, p=0.006) and were increased in patients with stable disease (p=0.02). These findings support the hypothesis that TIL characteristics may significantly affect mTNBC outcomes. We demonstrate that, although metastases have reduced immune presence, a higher CD8:FOXP3+ T cells may indicate a better prognosis in the metastatic setting. Furthermore, the correlation between CD8+ and FOXP3+ cells in metastases across sites, not observed in primary tumors, suggests that immunogenicity in metastases may be governed by different mechanisms than those in primary tumors, possibly contributing to the therapy resistance and worse outcomes observed in metastatic setting. The increased presence of FOXP3+ cells in metastases with high CAF levels suggests that metastatic CAFs promote an immunosuppressive environment, highlighting them as potential therapeutic targets. By identifying CAF-derived factors associated with increased FOXP3+ cell presence, novel therapies may help to overcome immunosuppression, enhance the cytotoxic immune response, and improve treatment efficacy in mTNBC.
Citation Format: Alexandra D. Goudreau, Alexandre Penoit, Jade Marie Lasiste, Olga Aleynikova, Khaled Katergi, Josiane Lafleur, Adriana Aguilar-Mahecha, Mark Basik. Primary and metastatic tumors from triple negative breast cancer possess distinct immunological profiles [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr B025.