ESR1 and breast cancer: ERs contain ERα and ERβ (Nilsson et al., 2011), in which ERα activated for proliferation of breast and uterine tissues (Frasor et al., 2003; Helguero et al., 2005) was overexpressed in more than 70% of breast cancers (Holst et al., 2007), thus ERα is the an important target for treating ERα positive breast tumor (Qin et al., 2018).