Esophageal and gastric cancers represent tumors with poor prognosis. Unfortunately, radiotherapy, chemotherapy, and targeted therapy have made only limited progress in recent years in improving the generally disappointing outcome. Immunotherapy with checkpoint inhibitors is a novel treatment approach that quickly entered clinical practice in malignant melanoma and renal cell cancer, but the role in esophageal and gastric cancer is still poorly defined. The principal prognostic/predictive biomarkers for immunotherapy efficacy currently considered are PD-L1 expression along with defects in mismatch repair genes resulting in microsatellite instability (MSI-H) phenotype. The new molecular classification of gastric cancer also takes these factors into consideration. Available reports regarding PD-1, PD-L1, PD-L2 expression and MSI status in gastric and esophageal cancer are reviewed to summarize the clinical prognostic and predictive role together with potential clinical implications. The most important recently published clinical trials evaluating checkpoint inhibitor efficacy in these tumors are also summarized.

• Keywords
• checkpoint inhibitors, esophageal cancer, gastric cancer, immunotherapy, microsatellite instability,
• MeSH
• Programmed Cell Death 1 Ligand 2 Protein metabolism   MeSH
• B7-H1 Antigen metabolism   MeSH
• Programmed Cell Death 1 Receptor metabolism   MeSH
• Epithelial-Mesenchymal Transition MeSH
• Gene Expression MeSH
• Phenotype MeSH
• Immunity * MeSH
• Immunotherapy * methods   MeSH
• Combined Modality Therapy MeSH
• Humans MeSH
• Microsatellite Instability MeSH
• Microsatellite Repeats MeSH
• Esophageal Neoplasms diagnosis   genetics   immunology   therapy   MeSH
• Stomach Neoplasms diagnosis   genetics   immunology   therapy   MeSH
• Tumor Escape immunology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Programmed Cell Death 1 Ligand 2 Protein MeSH
• B7-H1 Antigen MeSH
• Programmed Cell Death 1 Receptor MeSH