Different BC subtypes have been identified and correlate with metastatic potential and overall survival, with Triple Negative Breast Cancer (TNBC) having the worst prognosis due to the inefficiency of Estrogen Receptor (ER), Progesterone Receptor (PR) and Human Epidermal Growth Factor Receptor 2 (HER2) targeted therapies (13). The gene discussed is ESR1; the disease is breast cancer.