Dysbiosis of Oral Microbiome; A Key Player in Oral Carcinogenesis? A Critical Review

The oral cavity is known to harbor hundreds of microorganisms from various genera, constituting a peculiar flora called the oral microbiome. The change in the relative dis-tribution of the constituents of this microbial flora, due to any reason, leads to oral dysbiosis. Oral dysbiosis has been linked to the aetiopathogenesis of several medical illnesses, both locally and systemically, for centuries. Recently, aided by the advent of biotechnological capabilities, several reports have emerged on the role of oral dysbiosis in oral carcinogenesis, and numerous studies are currently exploring their association and plausible mechanisms. Some of the proposed mechanisms of oral dysbiosis-induced carcinogenesis (ODIC) include—bacteria induced chronic inflammatory state leading to direct cellular damage and inflammatory cytokines mediated promotion of cellular pro-liferation and invasion,—release of bacterial products that are carcinogenic, and—sup-pression of local immunity by altering the tumor microenvironment. However, the actual interactions between these cellular mechanisms are not yet fully understood. This review provides a comprehensive overview of the various hypotheses and mechanisms impli-cated in the ODIC, along with the corresponding molecular aberrations. Apart from discussing the usual constituents of the oral microbiome profile, the review also sum-marizes the various dysbiosis profiles implicated in ODIC. The review sheds light on the potential clinical implications of oral microbiome in the prevention, management, therapeutic responsiveness, and survival outcomes of oral cancer.