ERBB2 and gastric cancer: In contrast, immunohistological determination for the HER2 expression or the detection of a HER2 gene amplification by means of chromogenic or fluorescence in situ hybridization (CISH/FISH) are already among the established biomarkers in advanced/metastatic gastric cancer (Lordick et al. 2022a; Nagtegaal et al. 2020; Stahl et al. 2022) and adenocarcinomas of the esophagus and gastroesophageal junction (Obermannová et al. 2022; Quezada-Marín et al. 2010).