ESR1 and invasive breast carcinoma: Gallen International Consensus Conference (2023), the molecular classification of invasive breast carcinoma has been divided into four main subtypes based on the expression of immunohistochemical markers, including estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and Ki-67, which is an indicator of cell proliferation (2).