Based on the hormonal receptors, breast cancer can be categorized as a luminal subtype [estrogen receptor-positive (ER+) or progesterone receptor-positive (PR+)], a Her2-enriched subtype (Her2+; overexpressed Her2 receptor), and triple-negative (TNBC)/basal-like subtype (ER−, PR−, and Her2). Here, ESR1 is linked to breast cancer.