ERBB2 and gastric carcinoma: Due to the high intratumoral heterogeneity of gastric carcinoma and the focal nature of HER2 staining in up to 30% of cases (Bang et al. 2010; Rüschoff et al. 2010, 2012; Warneke et al. 2013), the experts recommend taking biopsies from different areas of the tumor to ensure that representative material is obtained sufficiently and to avoid false negative results.