ESR1 and breast cancer: To further prove this, we first investigated the protein levels of vimentin in the normal breast epithelial cell line, M10, as well as breast cancer cell lines with various levels of malignancy, such as MCF7, MDA-MB 468, and MDA-MB 231, which represented the cell lines at various stages: luminal (ER positive), basal-A (ER negative), and basal-B (ER negative and EMT phenotype) subtypes, respectively [32].