Breast cancer cell lines are considered as an infinite source of a homogeneous cell populations reflecting the main clinical types of breast cancer based on receptor status, e.g., estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-positive, and triple negative (TNBC, ER-negative, progesterone receptor (PR)-negative, and HER2-negative) subtypes [3]. This evidence concerns the gene PGR and breast cancer.