Abstract 2822: Single-cell evaluation to identify tumor-stroma niches driving the transition from in situ to invasive breast cancer
Authors: Sinha Vidya C. , Xu Mingchu , Rinkenbaugh Amanda L. , Zhou Xinhui , Zhang Xiaomei , Piwnica-Worms Helen 
Published: September 2020

Abstract
Introduction: Ductal carcinoma in situ is a non-invasive lesion of the breast that comprises ~20% of newly diagnosed breast cancers in the United States. Prospectively distinguishing indolent from aggressive lesions has been a major clinical challenge. To begin addressing these challenges, we use an experimentally tractable mouse model of breast cancer in which invasive (but rarely in situ) lesions display architectural and morphological abnormalities while also being heavily immune-infiltrated.
Methods: To explore the tumor-stroma niches that evolve as breast cancer progresses, we are undertaking single cell RNA sequencing and imaging mass cytometry to identify tumor and immune cells present within in situ (early) versus invasive (advanced) lesions, and to characterize shifts in phenotype and tumor-stroma niches that may occur as breast cancer transitions from in situ to invasive disease.
Results: Single cell analyses revealed major cell populations within the tumor compartment of both early and advanced disease, including luminal- and basal-like populations, as well as an additional minor population that appears to represent a unique intermediate between luminal and basal states. Early stage lesions were comprised primarily of the major luminal population, whereas advanced lesions exhibited a significant expansion of intermediate and basal populations, suggesting that breast cancer cells may undergo a transition from luminal-like to basal-like phenotype during progression to invasive disease. Analysis of the immune compartments of early versus advanced disease also revealed that the relative neutrophil/MDSC/S100A8+ population increased as lesions advanced, while B cells, NK cells, and some T cells decreased. Furthermore, the immune populations of advanced lesions exhibited widespread upregulation of IL-17 targets, suggesting that the IL-17 pathway may drive shifts in the immune microenvironmental to support disease progression, particularly the increase in neutrophils/MDSCs. Additionally, given a previously reported role of IL-17 to alter epithelial stemness, increased IL-17 signaling in advanced lesions may also be driving the potential luminal-to-basal transition of malignant cells.
Conclusion: Taken together, these findings suggest that a subset of malignant epithelial cells may transition from luminal-like to basal-like cells, and that this transition may be driven and/or maintained by a commensurate increase in IL-17 signaling that both directly impacts tumor cells and also establishes a tumor-supportive microenvironment.
Citation Format: Vidya C. Sinha, Mingchu Xu, Amanda L. Rinkenbaugh, Xinhui Zhou, Xiaomei Zhang, Helen Piwnica-Worms. Single-cell evaluation to identify tumor-stroma niches driving the transition from in situ to invasive breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2822.