ESR1 and breast carcinoma: Metastatic breast cancer (MBC) develops in 30%–40% of patients with breast carcinoma and patients with MBC have a median survival of about 2 years and, therefore, new anticancer agents are urgently required.75 Chemotherapeutic drugs are applied to patients depending upon size, lymph node status, ER and PR, and HER-2/neu over-expression.