Clinically, based on the expression of hormone receptors: estrogen receptor (ER), progesterone receptor (PR) and HER2 (human epidermal growth factor receptor 2, ERBB2), breast cancer is classified into three major subtypes: Luminal, HER2-enriched and triple-negative breast cancer (TNBC) [22]. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.