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. The gene discussed is ERBB2; the disease is neoplasm.