As a heterogenous malignancy, it could be divided into three categories according to molecular features, including hormone-positive subtype expressing estrogen receptor (ER+) or progesterone receptor (PR+), HER2-positive subtype expressing human epidermal receptor 2 (HER2+), and triple-negative breast cancer (TNBC) (ER-, PR-, HER2-) [52]. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.