PGR and breast cancer: According to gene expression profiles, BC subtypes can be classified into at least three subtypes: luminal tumors, which are positive for estrogen and/or progesterone receptors (ER/PgR); HER2-enriched, which overexpress the ERBB2 oncogene (HER2); and basal like, also known as triple negative tumors (TNBC), which lack hormone receptors and HER2 amplification [3].