PGR and breast cancer: For this study, three human BC cell lines were selected to represent the main BC subtypes: (1) MCF7: ER+, PR+, and HER-2−, corresponding to the most common BC type-Luminal A, (2) SKBR3: ER−, PR–, and HER-2+ representing the HER-2 BC subtype [38,39], and (3) MDA-MB-231, a “triple-negative cell line” (ER−, PR−, HER-2−), corresponding to the basal type breast carcinoma cell [38,40].