According to receptor status, molecular subtypes are broadly classified into four types, Luminal A (ER- or PgR- positive, HER2-negative), Luminal B (ER- or PgR-positive, HER2-positive), HER2-positive and TNBC, and are known to be key factors in determining the treatment strategy in early breast cancer patients [55,56]. Here, ESR1 is linked to breast cancer.