ERBB2 and gastric cancer: From a diagnostic perspective, ERBB2/HER2 assessment must encompass both protein and gene level: IHC is used to semi-quantitatively score membranous overexpression (0/1+/2+/3+) as initially established for gastric cancer [15], IHC 2 + cases require confirmatory in-situ-hybridization, typically fluorescence in situ hybridization (FISH) for ERBB2 amplification.