In brief, tumors expressing ER in the absence of HER2 (ER+/HER2−) are often classified as luminal subtype (A or B) [5], tumors with HER2 expression are often of HER2−enriched subtype, whereas tumors with higher proliferation while lacking the three receptors, also denominated triple negative breast cancers (TNBC), are often classified to the basal-like subtype [6]. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.