ESR1 and breast carcinoma: The “gold standard” treatment for this subtype of breast carcinoma is endocrine therapy (or anti-estrogen therapy), which is designed to block the estrogen receptor signaling pathway through Selective Estrogen Receptor Modulators (SERM) (Tamoxifen and Raloxifene), Selective Estrogen Receptor Down-regulators (SERD) (Fulvestrant) and Aromatase Inhibitors (Anastrozole) [1].