PGR and breast cancer: This effect was notably observed in various types of breast cancer cells: estrogen receptor-positive cells (ZR75.1); estrogen and progesterone receptor-positive cells (MCF-7); estrogen, progesterone, and HER2 receptor-positive cells (HCC-1954); and triple-negative breast cancer (TNBC) cells lacking any of these receptors (MDA-MB-231, SUM-149).