ESR1 and breast carcinoma: In routine practice, breast carcinoma is classified according to the status of four prognostic and predictive biomarkers, namely estrogen receptor (ER), progesterone receptor (PR), proliferation marker Ki67 and human epidermal growth factor receptor 2 (HER2/Neu) into luminal A, luminal B, HER2 positive (HER2 +) and triple negative (TNBC) [2].