A major challenge in the treatment of breast cancer is its high heterogeneity from patient to patient, which initiated its classification into three major molecular subtypes—estrogen receptors (ER), progesterone receptors (PR), and HER2, hormone receptor positive with luminal A (ER+PR+HER2−) and luminal B (ER+PR+HER2+) phenotypes, HER2 positive (ER−PR−HER2+), and triple negative/basal-like (ER−PR−HER2−) [80,81,82]. This evidence concerns the gene ESR1 and breast carcinoma.