The role of <i>Fusobacterium nucleatum</i> in the tumour microenvironment and carcinogenesis of oral and colonic malignancies

The intra-tumoural microbiome is an increasing area of research with potential benefits in cancer diagnostics and treatment development. Numerous studies have implicated <i>Fusobacterium nucleatum</i>, a member of the oral microbiota, in the development, immune evasion, and dissemination of oral and colorectal tumours. Although <i>F. nucleatum</i> is yet to be classified as a cause or consequence of cancer, reports indicate the microorganism's involvement in DNA damage, pathologic glucose uptake, and cellular proliferation. This accumulation of genetic instability is consistent with the multistep nature of malignant neoplasm progression. Virulence factors of <i>F. nucleatum</i> were shown to maintain an unresolved inflammatory state and impair the normal function of immune cells. The accompanying pro-inflammatory conditions facilitate vasculature remodelling, expediting tumour expansion, through a range of mechanisms. Pro-metastatic epithelial-to-mesenchymal transition and changes in gene expression have been observed in cancer cells upon <i>F. nucleatum</i> infection, suggesting an association with poorer prognosis. As a frequently encountered microorganism in the oral and colorectal intra-tumoural microbiome, <i>F. nucleatum</i> represents an intriguing, yet cautious research prospect with opportunities for novel prevention and therapeutic strategies. The objective of this work is to review the relevant evidence, taking into account the complexity of the tumour microenvironment.