These classifications include luminal A (ER and/or PR+, HER2-, Ki-67 <20%); luminal B (HER2-negative type/B1: ER+ and/or PR <20%, HER2-, Ki-67 ≥20%; HER2-positive type/B2: ER+ and/or PR+, HER2 overexpression); HER2-positive type (ER- and PR-, HER2+); triple-negative type (ER- and PR-, HER2-); and other specific types of breast cancer (3). Here, ESR1 is linked to breast cancer.