Breast cancer comprisesvarious genetic and epigenetic factors with explicit clinical implications.1,2 Different types of breast cancer are usually described by theirdependence on the estrogen receptor, ER, progesterone receptor, PR,and/or human epithelial receptor 2, HER2, with ER positive (ER+) casesaccounting for 75% of all cases.3 SinceER receptors are dysregulated in cancer cells, they are involved inuncontrolled cell proliferation, metastasis, and cancer invasiveness.4 Consequently, antagonizing ER receptors is partof the first-line therapy for ER+ breast cancer cases. This evidence concerns the gene ESR1 and breast cancer.