The classification of breast cancer encompasses four intrinsic molecular subtypes: Luminal A (expressing progesterone and estrogen receptors), Luminal B (displaying variable proliferation and a lack of human epidermal growth factor receptor 2 (HER2), while still expressing progesterone and estrogen receptors), HER2-overexpressing (HER2+), and basal-like breast cancer (expressing genes of normal breast basal and/myoepitelial cells) which are mostly triple-negative breast cancer; (TNBC) lacking expression of estrogen receptors (ER), progesterone receptors (PR), and HER2 [2,3]. The gene discussed is ESR1; the disease is breast carcinoma.