In this way, estrogen (ER) and progesterone receptor (PR)+/HER2- tumors are classified as belonging to the luminal A molecular subtype, ER+/PR+/HER2+ tumors to the luminal B subtype, ER-/PR-/HER2+ tumors to the HER2 subtype, and triple negative (ER-/PR-/HER2-) tumors to the basal-like carcinomas [8]. The gene discussed is ESR1; the disease is carcinoma.