Triple-negative breast cancer (TNBC) represents approximately 15% of all breast cancers and is a subtype distinguished by lack of expression of the estrogen and progesterone receptor by immunohistochemistry (IHC) and by the lack of overexpression and/or amplification of HER2 obtained with IHC and or fluorescence in situ hybridization (FISH). Here, PGR is linked to breast cancer.