Of note, ERK1/2 up-regulated the expression, phosphorylation, and transcriptional activity of ERRγ and caused ERRγ-mediated resistance to tamoxifen in ER+ breast cancer cells [96], alluding to the potential of EGFR-ERK1/2 inhibition together with ERR antagonists for hormone-based targeted therapies in patients. This evidence concerns the gene ESR1 and breast cancer.