The identification of tumors with HER2 overexpression is determined as a 3+ IHC score, which reflects strong membranous reactivity in at least 10% of cancer cells, or a 2+ IHC score and FISH/ISH positivity (indicated by a HER2:CEP17 ratio of ≥2 or an average HER2 copy number of ≥6 signals/cell). The gene discussed is ERBB2; the disease is cancer.