One study described the high incidence of intratumoural HER2 heterogeneity in a large series of 322 patients with GC in detail by performing HER2 immunohistochemistry (IHC) and fluorescence in situ hybridisation (FISH) and evaluating the gene copy number individually in distinct areas with different IHC staining intensity. This evidence concerns the gene ERBB2 and gastric cancer.