Current Evidence on the Relation Between Microbiota and Oral Cancer-The Role of Fusobacterium nucleatum-A Narrative Review

Oral squamous cell carcinoma (OSCC) is one the most prevalent head and neck cancers and represents a major cause of morbidity and mortality worldwide. The main established risk factors for OSCC include tobacco and alcohol consumption and betel quid chewing, which may contribute alone or in combination with other environmental factors to carcinogenesis. The oral microbiota is emerging as a key player in the establishment of the molecular and cellular mechanisms that may trigger or promote carcinogenesis, including in the oral cavity. Among the bacterial species found in the oral microbiota, Fusobacterium nucleatum, an anaerobic bacterium commonly found in oral biofilms and a periodontal pathogen, has gained attention due to solid evidence implicating F. nucleatum in colorectal cancer (CRC). F. nucleatum has been shown to induce chronic inflammation, promote cell proliferation and trigger cellular invasion while deploying immune evasion mechanisms. These experimental findings were first obtained in in vitro and in vivo models of CRC and are being confirmed in studies on OSCC. In this review, we summarize the most recent findings on the role of F. nucleatum in OSCC, discuss the clinical implications in terms of prognosis and provide an overview of the key mechanisms involved. Moreover, we identify research questions and aspects that require investigations to clarify the role of F. nucleatum in OSCC. We anticipate that studies in this emerging field may have a significant clinical impact on the diagnosis, prognosis and management of OSCC.