The Role of Microbiota in Upper Gastrointestinal Cancers

The gut microbiota significantly impacts the development and progression of upper gastrointestinal (GI) cancers, including esophageal and gastric cancers. Microbial dysbiosis contributes to carcinogenesis through mechanisms such as inflammation, immune modulation, and direct DNA damage. Techniques for sampling oral, esophageal, and gastric microbiota vary, with standardization being essential for reliable results. Barrett’s esophagus (BE) and esophageal adenocarcinoma (EAC) are associated with an enrichment of Gram-negative bacteria, promoting inflammation and cancer progression. Esophageal squamous cell carcinoma (ESCC) also shows distinct microbial patterns, with reduced diversity and increased harmful bacteria like Porphyromonas gingivalis and Fusobacterium nucleatum. In gastric cancer (GC), Helicobacter pylori (HP) and non-HP gastric microbiota play significant roles, with diverse microbial communities contributing to cancer development through nitrate reduction, immune modulation, and inflammation. Emerging evidence highlights the role of non-HP bacteria in promoting carcinogenesis, with specific taxa like Fusobacterium nucleatum and Lactobacillus influencing tumor growth and immune evasion. Further research is needed to elucidate the complex interactions between gut microbiota and upper GI cancers, paving the way for novel diagnostic and therapeutic approaches. Understanding these microbial dynamics offers potential for microbiota-based interventions, improving the early detection, prognosis, and treatment of upper GI cancers. This comprehensive review summarizes the available evidence on the role of microbiota in upper GI oncology and the need for continued exploration in this field.