Intratumoral Fusobacterium nucleatum Drives Cancer-Associated Fibroblasts Enrichment and Immune Exclusion in Esophageal Squamous Cell Carcinoma

Background: Fusobacterium nucleatum, an oral commensal bacterium, has been increasingly recognized for its oncogenic role in gastrointestinal malignancies. In esophageal squamous cell carcinoma (ESCC), F. nucleatum has been implicated in promoting tumor progression and facilitating immune evasion. However, its relationship with stromal remodeling and the tumor microenvironment (TME) remains unclear. Methods: We performed integrative analyses using metagenomic profiling and transcriptomic deconvolution, and histopathological assessment of 93 The Cancer Genome Atlas (TCGA)-ESCC cases and an independent cohort of 126 resected tumors. F. nucleatum status was determined by microbial abundance and quantitative Polymerase Chain Reaction (q-PCR). Results: F. nucleatum-positive tumors showed significant enrichment of TNFα/NF-κB signaling and reduced CD8⁺ T cell infiltration. Stromal analysis revealed a marked increase in cancer-associated fibroblasts (CAFs) in F. nucleatum-positive tumors, confirmed by transcriptomic deconvolution and α-SMA immunohistochemistry. Notably, immunohistochemical analysis demonstrated increased nuclear localization of NF-κB p65, indicating F. nucleatum-induced NF-κB activation in tumor cells. Clinically, among elderly patients with poor performance status, the prevalence of F. nucleatum positivity was significantly higher. Conclusion: F. nucleatum may contribute to the progression of ESCC by inducing NF-κB–mediated inflammatory signaling in tumor cells and promoting CAFs activation. Its presence may facilitate immune exclusion and tumor invasion through stromal remodeling. Furthermore, F. nucleatum positivity may reflect broader host vulnerability, particularly in frail elderly individuals. These findings highlight F. nucleatum as a potential biomarker of tumor immune dynamics and suggest the importance of maintaining good oral hygiene to reduce F. nucleatum colonization.