Currently, HER2 positivity in breast tumors is defined by the overexpression of HER2 protein measured using immuno-histochemistry (IHC3+) and/or in situ hybridization (ISH) (HER2 gene copy number ≥6 or a HER2/CEP17 ratio ≥2.0) (6, 7). The gene discussed is ERBB2; the disease is breast neoplasm.