ESR1 and breast cancer: The 2011 European Society of Medical Oncology breast cancer clinical practice guideline required a preoperative disease-related staging, including pathological examination of the CNB with a report on estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor receptor-2 (HER2) status by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH) [3].