PGR and breast cancer: In breast cancer cell lines and in tumor breast cells, particularly those with a “triple negative” (TNBC, triple negative breast cancer) phenotype (so defined because tumor cells do not express the estrogen receptor (ER), progesterone receptor (PR) and the HER2 isoform of the epithelial growth factor receptor, EGFR [52]), AhR cooperates with NF-κB.