BC are clinically stratified based on estrogen receptor (ER), progesterone receptor (PR), and HER2 expression into three major subtypes namely: Luminal (ER+, PR+/−), HER2+ (HER2+, ER+/−, PR+/−) and triple negative (TNBC; ER−/PR−/HER2−) correlating with prognosis where the expression of those biomarkers plays essential role in defining treatment strategies [2]. The gene discussed is ESR1; the disease is breast cancer.