Luminal A breast cancer (LumABC) is a molecular subtype of breast cancer that is distinct from other subtypes, characterized by high expression of estrogen receptor (ER) and/or progesterone receptor (PR), low expression of human epidermal growth factor receptor 2 (HER2), and a low proliferation index, such as Ki-67 [2]. The gene discussed is ESR1; the disease is breast carcinoma.