ERBB2 and cancer: According to ASCO/CAP guidelines, HER2 positivity is defined as a complete and strong membrane staining resulting in a IHC score of 3+ in ≥10% of cancer cells, and/or amplification of the ERBB2 gene detected with in situ hybridization (ISH) techniques with a HER2/CEP17 ratio cutoff of ≥2.0 and an average HER2 gene copy number ≥4.0 signals/cells [3].