ESR1 and breast carcinoma: Since 2000, breast cancer has been categorized into distinct molecular types based on the expression levels of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), which is ER-positive/luminal-like, Erb-B2 positive, basal-like, normal breast-like and claudin-low, paving the way for personalized, effective and safe treatments (3–6).