These subtypes consist of Luminal A (low grade, ER+/PR+, HER2-, low Ki67), Luminal B (ER+/PR+, HER2+ or HER2-, high Ki67), TNBC or basal-like (ER-/PR- and HER2-), HER2-enriched and normal-like breast cancer [128]. The gene discussed is ESR1; the disease is breast carcinoma.