Subtypes of breast cancer are classified by the presence of hormone receptors (including estrogen ER and progesterone PR receptors), human epidermal growth factor receptor 2 (Her2 status) as based on a subdivision on luminal A and luminal B, and triple-negative (ER-, PR-, HER2-) [9,10,11,12,13] [Figure 1]. This evidence concerns the gene ESR1 and breast cancer.