Microbes live within a complex ecosystem in the human oral cavity and other body habitats involving well over 1,000 different types of bacteria, archaea, eukarya, fungi, and viruses. While the majority of microorganisms exist within the oral cavity in a symbiotic relationship with the host, perturbations of the host-microbiota interaction may lead to oral and pharyngeal disease, including cancer.
We are just beginning to understand the degree to which indigenous microbiota and viruses increase the risk of malignancy, including oral and pharyngeal malignancies. New sequencing technologies permit the characterization of complex microbial communities that might be involved in oral health and disease.
Results from recent investigations using 16S rRNA gene tag pyrosequencing suggest that 250-300 bacterial phylotypes inhabit the mouth of healthy individuals. Protection against oral infectious diseases is gained through competition between commensal and pathogenic symbionts for mucosal surfaces. Such competition between species not only dampens the risk of disease, but also reduces the concentration of proinflammatory cytokines elicited during infection. Pathogens and commensals in the oral cavity evade the immune response by forming biofilms that are resistant to host clearance. While several small studies suggest differences in the oral microbiome between oral and pharyngeal cancer patients and healthy controls, specific causal pathogens have yet to be identified.
Recent research provides evidence for an increasing percentage of oropharynx cancers attributable to HPV infection. It is likely that other infectious agents may also contribute to the risk of oral and pharyngeal malignancy.