These subtypes were classified as follows (1): luminal A (estrogen receptor (ER)+/progestogen receptor (PR)+/HER2 receptor−) (2); luminal B (ER+/PR+/HER2+) (3); human epithelial factor receptor (HER)2 positive (ER−/PR−/HER2+); and (4) basal-like (75% belong to triple-negative breast cancer, ER-/PR-/HER2-). Here, ESR1 is linked to triple-negative breast carcinoma.