ESR1 and breast cancer: Likewise, upon estrogenic stimulation, ERα engages tyrosine kinase receptors as IGF1R, the EGF receptor, and ErbB2 (HER-2/neu), triggering relevant biological effects in diverse cell contexts, including BC cells (Kahlert et al., 2000; Chung et al., 2002; Razandi et al., 2003).