ESR1 and breast cancer: Overall, the aforementioned nuclear and extranuclear-initiated pathways driven by ERα may control a variety of biological outcomes in mammary tumor cells, ranging from cell cycle, proliferation, chromatin remodeling to survival, and motility (Ballaré et al., 2003; Levin, 2003; Qiu et al., 2003; Castoria et al., 2004; Vicent et al., 2006; Giretti et al., 2008; Levin and Pietras, 2008; Giovannelli et al., 2012).