Triple-negative breast cancer (TNBC) is the least common type of breast cancers, accounting for 10–15% of all cases, but is often more aggressive and difficult to treat due to the lack of efficient molecular targets, such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) [1]. The gene discussed is ESR1; the disease is breast cancer.