These major subtypes including (i) epidermal luminal A (ER+, PR+/− and HER2−), (ii) Luminal B (ER+, PR+/− and HER2+), (iii) HER2 (ER−/PR− and HER2+), and (iv) Triple-negative (ER−, PR−, HER2−) or basal-like breast cancers. Here, ESR1 is linked to breast cancer.