ESR1 and triple-negative breast carcinoma: Triple-negative breast cancer (TNBC) comprises approximately 15% of all breast tumors and is characterized by a lack of ER, PR, and ERBB2 expression, which conveys a higher risk of distant metastasis compared to the other two subtypes, collectively referred to as non–triple-negative breast cancer (nTNBC) (Foulkes et al., 2010).