ESR1 and breast carcinoma: In breast cancer, estrogen receptor (ER), progesterone receptor (PR), and Erb-b2 receptor tyrosine kinase 2 (ERBB2, previously named Human Epidermal Growth Factor 2 or HER2 or HER-2/neu2) are biomarkers known to be related to tumor growth and prognosis, and assessing their expression is necessary to define therapeutic management (3–7).