Localization of Fusobacterium nucleatum in oral squamous cell carcinoma and its possible directly interacting protein molecules: A case series.

INTRODUCTION: While 15 to 20% of cancers are associated with microbial infection, the relationship between oral microorganisms and oral squamous cell carcinoma (OSCC) remains unclear. The location of bacteria in a tumor is closely related to its carcinogenic mechanism. The aim of this study was to analyse bacterial diversity in clinical OSCC tissue samples and tumor distant normal tissues, locate target bacteria, and search for proteins that may interact with target bacteria. MATERIALS AND METHODS: The 16S rDNA method was used to analyse bacterial diversity in clinical OSCC tissue samples and tumor distant normal tissues. Correlations between Fusobacterium abundance and clinicopathological characteristics were analysed using the χ2 test. The position of target bacteria was analysed by fluorescence in situ hybridization (FISH), and the expression of CK, CD31, CD45, CD68, cyclin D1, ß-catenin, E-cadherin, NF-κB, and HIF-1α was analysed by immunohistochemistry (IHC) in OSCC tumor tissues and tumor distant normal tissues. RESULTS: The 16S rDNA results showed that the detected amount of Fusobacterium in OSCC tumor tissues was significantly larger than that in tumor distant normal tissues. High expression of Fusobacterium was significantly correlated with the lifestyle-related oral risk habits, including smoking (p=0.036) and alcohol consumption (p=0.022), but did not correlate with patient sex, age, tumor laterality, tumor size, grade or TNM stage. Fusobacterium nucleatum was enriched in tumor stroma, where CD31+ blood vessels and inflammatory cells (including CD45+ leukocytes and CD68+ macrophages) were densely distributed. Cyclin D1 was mainly expressed in the nucleus of tumor cells. ß-catenin was expressed in the tumor cell membrane and was positively expressed in tumor interstitial vascular endothelial cells. E-cadherin was mainly expressed in tumor cell membranes. NF-κB was positively expressed in the cytoplasm of tumor cells, tumor interstitial cells and myo-fibrocytes. HIF-1α was mainly expressed in the cytoplasm of tumor interstitial cells. HIF-1α was highly expressed where Fusobacterium nucleatum was densely distributed. CONCLUSION: According to our study, the detected amount of Fusobacterium in OSCC tumor tissues was significantly larger than that in tumor distant normal tissues, and Fusobacterium nucleatum might aggravate inflammation and hypoxia by interacting with NF-κB and HIF-1α in OSCC.