The subtypes of BC are Luminal A (ER-positive, HR-positive, and HER2-negative), luminal B (ER-positive, PR-negative, and HER2-positive), HER2 overexpressing, normal-like breast cancer, and basal-like/triple-negative breast cancer (ER-negative, HER2-negative, and PR-negative). Here, ESR1 is linked to breast cancer.