The molecular characterization of BC has helped identify four different intrinsic subtypes: luminal A and luminal B (expressing ER and/or PR) and human epidermal growth factor receptor 2 (HER2)‐enriched and basal‐like, which expresses certain markers of basal cellular origin, but not ER, PR, and HER2.29 The gene discussed is ESR1; the disease is breast cancer.