It is a heterogeneous malignancy, and distinct molecular subtypes have been characterized, including the Luminal A subgroup expressing the hormone receptors estrogen receptor (ER) and progesterone receptor (PR); the Luminal B type expressing ER and PR plus human epidermal growth factor receptor 2 (HER2); the HER2-positive type (HER2+/ER−/PR−); and triple-negative breast cancer (TNBC; ER−/PR−/HER2−). Here, ESR1 is linked to triple-negative breast carcinoma.