[Biomarker testing for carcinomas of the upper gastrointestinal tract].

Predictive biomarker testing is nowadays an integral part of modern diagnostics and treatment planning for esophageal and gastric cancer. It currently consists mainly of immunohistochemically determined markers, namely the PD-L1 status (stated by the Tumor Proportion Score [TPS], Combined Positivity Score [CPS] and Tumor Area Proportion [TAP] Score) in esophageal squamous cell carcinomas, as well as the HER2 status (supplemented by in situ hybridization in case of equivocal results), the mismatch repair status (optionally supplemented by molecular pathological determination of microsatellite status), and, since mid-2024, the expression of claudin 18.2 in gastroesophageal adenocarcinomas. An expansion of the panel by FGFR2b is expected in the near future. In addition to the quality guideline-compliant technical performance of the tests, the biological heterogeneity of many of these biomarkers is also a diagnostic and clinical challenge. The current article provides an overview of current biomarker testing in the context of current treatment options for cancer of the upper gastrointestinal tract.