Fusobacterium nucleatum in cancer: prognostic relevance and clinical implications

Fusobacterium nucleatum (F. nucleatum) is a Gram-negative anaerobic bacterium of the normal human microbiota, originally identified in the oral cavity but now recognised as a constituent of the intratumoural microbiome across a broad range of human malignancies. This structured narrative review summarises the human evidence for F. nucleatum in different tumour entities. Within little more than a decade, F. nucleatum has become one of the most extensively characterised tumour-associated bacteria. Its DNA has been detected in every entity covered here, and in colorectal cancer a substantial and reproducible body of work links intratumoural F. nucleatum to shorter survival across independent cohorts, populations and detection platforms, increasingly resolved to subspecies and clade level. Evidence in other entities is younger and more heterogeneous: several show comparable associations, whereas in oral squamous cell carcinoma F. nucleatum positivity has been linked to improved outcomes. Rather than undermining the field, this heterogeneity points to a context-dependent biology shaped by tumour type and molecular subtype, specimen, detection method and threshold, and treatment setting. Mechanistic work provides a coherent basis for these observations. In experimental models, the adhesins FadA and Fap2 mediate interactions with host cells that promote proliferative signalling, immune evasion and metastatic spread, and bacterial depletion attenuates tumour growth - proof of principle for a targetable microbial component of the tumour. F. nucleatum is therefore a compelling candidate for microbiome-informed oncology. Realising this potential requires standardised assays, validated cut-offs and prospective trials.