ESR1 and triple-negative breast carcinoma: The continuous growth of the clonal subpopulations can effectively guide the cell differentiation into four varieties, including Luminal A (ER and/or PR positive and HER2 negative), Luminal B (ER and/or PR positive and HER2 positive), HER2-enriched (ER and PR negative, and HER2 positive), and Basal-Like (triple negative breast cancer ER, PR, and HER2 negative), in accordance with the expression of estrogen receptor (ER), progesterone receptor (PR), and overexpression of human epidermal growth factor receptor 2 (HER2/neu) [5, 6].