MDA-MB-231 is a well characterized metastatic breast cancer cell line isolated from pleural effusion of a patient with adenocarcinoma suffering from widespread metastasis, and is known as a ‘basal’ or ‘triple-negative’ cell line with stem cell-like or post-Epithelial-Mesenchymal Transition (EMT) features and fails to express estrogen receptors, progesterone receptors or human epidermal growth factor receptor 2 (HER2). This evidence concerns the gene ERBB2 and breast cancer.