Abstract

Metastatic breast cancer remains one of the most difficult cancers to treat, with a five-year survival rate that drops from 99% for localized disease to just 33% once distant metastases are present. This disparity reflects a fundamental gap in our understanding of how breast tumors spread and highlights the urgent need to improve our understanding of breast cancer metastasis to aid in development of novel therapeutics. Emerging evidence establishes that metastasis requires interactions between tumor cells and non-tumor stromal cells within the tumor microenvironment. The first aim of this dissertation investigates the role of Discoidin Domain Receptor 2 (DDR2), a collagen-binding receptor tyrosine kinase, in endothelial and lymphatic endothelial cells within the breast TME. While DDR2 has previously been implicated in breast cancer metastasis by promoting a migratory phenotype in tumor epithelial cells and cancer-associated fibroblasts (CAFs), its expression and function in endothelial cells has remained largely unexplored. We demonstrate that DDR2 is expressed by a subset of endothelial cells and lymphatic endothelial cells in human breast tumors. Using an endothelial cell-specific conditional knockout mouse model (Cdh5-CreERT2; Ddr2fl/fl) in the context of the MMTV-PyMT breast tumor model, we find that endothelial cell-intrinsic DDR2 is required for normal and tumor angiogenesis and contributes to breast tumor lung metastasis. Further, we developed and validated a novel microfluidic device assay to model endothelial cell migration in response to fluid flow. Using this system, we demonstrate that DDR2 regulates directed endothelial cell and lymphatic endothelial cell migration in response to fluid flow, providing insight into how DDR2 contributes to angiogenesis within the breast TME. The second aim of this dissertation investigates the contributions of CAFs to breast tumor collective migration. Collective migration occurs when tumor cells escape the primary tumor as cohesive clusters and gives rise to circulating tumor cell clusters. Although more rare, circulating tumor cell clusters have dramatically elevated metastatic potential when compared to single cell circulating tumor cells. Using primary breast tumor organoids and single-cell RNA sequencing, we identify two transcriptionally distinct CAF subpopulations within collectively migrating tumor clusters. Leveraging microfluidic chemotactic gradient systems, we demonstrate that CAFs enhance collective migration efficiency, may influence tumor cell aggregation, and the generation of leader cell identity at the invasive front. We further show that Cadherin-11, enriched in CAFs associated with migrating organoids, is required for CAF-mediated enhancement of collective migration, while Cadherin-2 is dispensable for this process. Together, this work reveals that two distinct stromal cell populations, endothelial cells and CAFs, actively promote breast tumor progression through angiogenesis and collective invasion, respectively. Importantly, these studies identify DDR2 as a novel endothelial cell-intrinsic regulator of tumor vascularization and metastasis, and identify Cadherin-11 as a CAF-specific mediator of invasive collective migration. These findings advance our understanding of tumor-stromal biology and highlight new stromal targets with potential therapeutic relevance for limiting breast cancer metastasis.

Committee Chair

Gregory Longmore

Committee Members

Amit Pathak; Jason Weber; Roberta Faccio; Sheila Stewart

Degree

Doctor of Philosophy (PhD)

Author's Department

Biology & Biomedical Sciences (Cancer Biology)

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

7-29-2026

Language

English (en)

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