ESR1 and breast carcinoma: Many breast cancer cell markers act as potential targets for the precise delivery of cancer chemotherapeutics which include overexpressed estrogen receptor (ER), progesterone receptor, HER2 receptor, folate receptor (FR), epidermal growth factor receptor (EGFR), transferrin receptor (TfR), integrin receptor, nucleolin receptor, CD44 receptor, etc. on the surface of breast cancer cells [53,54].