ERBB2 and gastroesophageal junction adenocarcinoma: These findings show that HER2, PD-L1 CPS, MSI, and claudin 18.2 are important biomarkers for the selection and efficacy prediction of first-line chemotherapy in patients with unresectable esophagogastric junction adenocarcinoma a, although claudin 18.2 IHC is not currently commercially available.