This belief is especially developed in oncology, where an increasing number of new targeted therapies are given only to a small selection of patients based on biomarkers [9]: examples are mutations that lead to upregulation of epidermal growth factor receptor (EGFR) in lung cancers [10], expression of erb-b2 receptor tyrosine kinase 2 (ERBB2, also known as HER2) in breast cancer [11], B-Raf proto-oncogene (BRAF) mutations in melanoma [12], and expression of the CD274 molecule known as Programmed death-ligand 1 (PD-L1) expression in various cancer types [13, 14]. The gene discussed is ERBB2; the disease is breast cancer.