THE ROLES OF EPITHELIAL–MESENCHYMAL PLASTICITY IN TUMOR HETEROGENEITY, METASTASIS, AND PATIENT SURVIVAL IN BREAST CANCER

The Epithelial-to-Mesenchymal transition, a critical cellular process in development, is frequently co-opted by solid tumors to promote invasion and metastasis. In particular, the hybrid or intermediate EMT state, possessing both epithelial and mesenchymal characteristics, is associated with increased cancer stemness and plasticity. Similarly, intra-tumoral heterogeneity in solid tumors, in particular breast cancer, is associated with poor prognosis, tumor growth, proliferation, drug resistance, and metastasis. We sought to understand the link between the generation of intra-tumoral heterogeneity and the intermediate EMT state and their impact on tumor progression and patient prognosis. As part of my thesis work, I developed a model to study EMT by isolating single cell-derived clonal populations along the EMT spectrum of cell states using the SUM149PT basal-like breast cancer cell line and validated the impact of intermediate EMT states on tumor progression and metastasis in an orthotopic mouse model. Using this model, I developed and tested a novel multiplexed multi-round staining approach to identify and quantify E-M heterogeneity and EMT score in breast cancer. These metrics were further validated with high reproducibility on a large cohort of breast cancer patient samples, while developing the approach in a high throughput-adaptable way for broad use. This comprehensive analysis highlighted the impact of high E-M heterogeneity and overall intermediate EMT scores on decreased overall survival in these patients. Further, we used the SUM149PT model to understand the driving transcriptional networks of the intermediate EMT and identified CBFb as a regulator of metastasis in the intermediate state by promoting tumor heterogeneity and stabilizing the intermediate EMT state. Taken in its totality, this work provides the further support for understanding intermediate EMT states and their roles in cancer metastasis and heterogeneity, a framework for comprehensive identification of E-M tumor heterogeneity in patient samples, and therapeutic targets that can help to reduce the presence of this tumorigenic and metastasis-promoting phenotype in patients