FN1 and breast cancer: The treatment of 4T1 breast cancer cells with TGF-β resulted in a fibroblast-like mesenchymal phenotype (Fig. 2a), accompanied by the appearance of the features of EMT, including upregulation of the mesenchymal marker fibronectin and downregulation of the epithelial marker E-cadherin, as determined by quantitative PCR (Fig. 2b).