ERBB2 and gastroesophageal junction adenocarcinoma: The National Comprehensive Cancer Network recommends trastuzumab combined with chemotherapy for HER2-positive gastric or GEJ adenocarcinoma and nivolumab combined with chemotherapy for HER2-negative and PD-L1 CPS ≥ 5 as first-line treatment.7 Therefore, it is important to obtain biomarker data, including prevalence rates and co-expression with other selected GC biomarkers.