ESR1 and neoplasm: The biomarkers defined by immunohistochemistry (IHC) for the diagnostic pathology of the breast [5] are the positive hormonal receptors, estrogen and the progesterone receptor (ER and PR, respectively), as well as, receptor 2 of human epidermal growth factor (HER2) and Ki67 cell proliferation index, which have been very useful to define the subrogated molecular phenotypes that guide with the aggressiveness of the tumor and treatment.