ESR1 and triple-negative breast carcinoma: Currently, breast cancers are classified into four molecular subtypes including, luminal A, luminal B, human epidermal growth factor receptor 2 (HER2) overexpressed, and triple-negative breast cancer (TNBC) subtypes according to estrogen receptor (ER), progesterone receptor (PR), and HER2 status by gene expression profiling [1, 2].