ESR1 and breast neoplasm: Estrogens, known to promote breast carcinogenesis (Liehr 2001), primarily act via two receptors, estrogen-receptor α (ER-α) and ER-β with ER-α being more abundantly expressed (Hewitt and Korach 2003) in approximately two-thirds of breast tumors and its presence determines the responsiveness towards hormone therapy (Williams et al. 2008).