ESR1 and breast cancer: Classic markers for breast cancer, such as Ki67, Estrogen Receptor (ER), Progesterone receptor (PR), Human epidermal growth factor receptor 2 (HER2), p53, ARF tumor suppressor (p14ARF), cyclin D1, cyclin E, T-box transcription factor 2 and 3 (TBX2/3), breast cancer type 1 and 2 (BRCA1/2), and vascular endothelial growth factor (VEGF)7 are no longer able to give a clear prognosis in the evolution of a patient’s disease and therefore other markers are currently being studied.