Abstract 5693: Cancer cells subvert fibroblast function to promote a growth factor enriched tumor microenvironment in endocrine therapy resistant ER+ breast cancer

Abstract

Abstract While endocrine therapy (ET) has considerably improved Stage II/III ER+ breast cancer survival rates, resistance emerges in 30-50% of patients. Recent advances have uncovered numerous cancer intrinsic and tumor-microenvironment mediated mechanisms contributing to ET resistance. However, the predominant mechanisms that prevent cure and ultimately lead to development of terminal metastatic cancer remain unknown. To reveal the leading causes of ET resistance in early-stage ER+ breast cancers, we used single-cell RNA sequencing to profile serial tumor biopsies from a larger cohort of patients. Patients received either endocrine therapy (letrozole) alone or in combination with a CDK4/6 cell cycle inhibitor (ribociclib). We examined the evolution of tumor composition, cellular communication, and the phenotypic diversity of tumor-associated cancer and non-cancer cells throughout treatment. Our analyses reveal that ET-resistant tumors are fibroblast- and endothelial-enriched and consistently exhibit broad upregulation of growth factor signaling to cancer cells, with consistent activation of ERBB communication across patient tumors. Fibroblasts emerged as the primary source of these additional growth factor signals. Upregulation of fibroblast growth factor signaling (via NRG1/2, EGF and IGF) was commensurate with differentiation to a mesenchymal cancer-associated-fibroblast (myCAF) phenotype, which was itself stimulated by cancer cells through EGF and TGF signaling. In response to growth factor enrichment, cancer cells of ET-resistant tumors showed activation of MAPK signal transduction and downstream transcription factors promoting proliferation including FOS, JUN and TRIB1. These results indicate that ET resistance emerges in patient tumors when cancer cells subvert fibroblast function to promote a growth factor enriched tumor microenvironment permitting estrogen independent cancer proliferation. Citation Format: Jason I. Griffiths, Patrick A. Cosgrove, Eric Medina Castaneda, Aritro Nath, Jinfeng Chen, Frederick R. Adler, Jeffrey T. Chang, Qamar J. Khan, Andrea H. Bild. Cancer cells subvert fibroblast function to promote a growth factor enriched tumor microenvironment in endocrine therapy resistant ER+ breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5693.