It is a heterogeneous disease classified under the following various subtypes: (i) luminal A and B (accounting for 50–60% of breast cancer cases); (ii) basal-like or triple-negative (TNBC) (10–20%), which lack the ER, PR, and HER2 receptors; and (iii) HER2 (human epidermal growth factor receptors, 10–15%) [3]. This evidence concerns the gene ESR1 and breast cancer.