PGR and breast cancer: Herein, we utilized two claudin-low triple-negative breast cancer ((oestrogen receptor (ER), progesterone receptor (PR), no human epidermal growth factor receptor 2 (HER2) overexpression); TNBC) cell lines (MDA-MB-231 and BT549) that are enriched for features associated with epithelial-to-mesenchymal transition (EMT) and ‘breast cancer stem cell phenotypes’14, 15, 16.