In addition to the inter-patient heterogeneity, across patients, of protein levels of established prognostic and predictive biomarkers (estrogen receptor, ER, progesterone receptor, PR, and human epidermal growth factor receptor 2, HER2) [2], the cells within each tumor are also diverse with respect to their somatic mutations, gene expression and epigenetic profiles, and proteomic and metabolic programming. This evidence concerns the gene ESR1 and neoplasm.