ESR1 and triple-negative breast carcinoma: Upon diagnosis, patients are classified into three main groups for treatment: (1) the hormonal receptor positive group (HR positive) characterized by estrogen receptor (ER) and/or progesterone receptor (PR) expression; (2) the human epidermal growth factor receptor 2 (HER2) amplified group, and; (3) the triple-negative breast cancer (TNBC) group, lacking expression of ER, PR and HER2.