ESR1 and neoplasm: The factors predicting disease course encompass both routinely assessed pathological (lymph node status, grading, tumour size and extent) and biological characteristics, predominantly the steroid hormone receptor status (Estrogen Receptor (ER), Progesterone Receptor (PR)), as well as human epidermal growth factor receptor 2 (HER2) expression/amplification status and Ki67 proliferation index [2].