ESR1 and breast carcinoma: Based on the expression of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2 (HER2), and Ki-67, breast cancer can be divided into the following types: the luminal (luminal or hormone receptor positive) A, luminal B, Her-2 overexpression, and basal-like (substrate) types (Viale et al., 2019).