Using the most common definition, breast cancer is divided into four molecular subtypes—luminal A, luminal B, HER2+, and triple negative breast cancer (TNBC)—based upon the presence or absence of important hormone receptors, including the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) (4). The gene discussed is ESR1; the disease is triple-negative breast carcinoma.