Indeed, the cross talk between ER pathways and growth factor receptor pathways (EGFR, IGF-1, and HER2) has been involved in cell proliferation, survival, and resistance to endocrine therapy (TAM) in breast cancer (Yager & Davidson 2006, Pietras & Marquez-Garban 2007, Chang 2011). This evidence concerns the gene ESR1 and breast cancer.