PGR and breast cancer: Since breast cancer(BC) is the most common malignancy worldwide [1], we further tested the mRNA and protein expression of CALR in immortalized breast epithelial cells (MCF-10A) and six different human BC cell lines, which encompassed the major clinical categories of BC based on expression of the estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2): MCF-7 is ER+PR+ HER2− (Luminal A molecular subtype); HCC1954 and MDA-MB-453 are ER−PR−HER2+ (HER2-enriched subtype), and MDA-MB-231, BT549 and SUM159 are ER−PR−HER2− (Basal-like subtype) [27].