RecruitingDiagnostic testComparison of Molecular-Genetic Concordance of the Primary Tumor and Brain Metastases of Gastroesophageal CancersGENCONCOR-2 is a translational research aimed to compare the molecular profile of primary tumors and their matched brain metastases in gastroesophageal cancers, including cancer of the esophagus, gastroesophageal junction, and stomach. The study is based on the previously established international GASTROBRAIN cohort (ClinicalTrials.gov ID: NCT07448493), which provides comprehensive clinicopathological and treatment data for over 230 patients. It will be conducted by retrospective analysis of paired samples of histological material (primary tumor and corresponding brain metastasis) with determination of HER2 expression status (IHC ± FISH), MSI status (IHC ± PCR), PD-L1 combined positive score (CPS), and CLDN18.2 expression status (IHC)