Role of Microbiome in the Etiopathogenesis of Head and Neck Cancer

The term microbiome was proposed to identify the microorganisms colonizing the human body. Since 2005, several programs, such as the Human Intestinal Metagenome Initiative, have improved our knowledge among the pathogenic mechanisms leading to cancer from chronic inflammation, particularly examining the possible role of viruses and bacteria. This chapter aims to revise the actual knowledge about the possible relationship between head and neck microbiome and cancer. The oral cavity presents the most varied microbiome of the head and neck regions, with more than 700 bacterial species. Also nasopharynx, pharynx, and larynx have a microbial population constituted from both saprophytes and pathogens. Many authors have suggested a possible role of chronic inflammation in the pathogenesis of head and neck cancer; different mechanisms have been proposed, since chronic inflation could lead to cellular DNA damages, inhibition of apoptotic pathways, abnormal cellular differentiation responsible of local cellular invasion and migration, and upregulation of cellular proliferation. Moreover, an active role of head and neck microbiome has been proposed in pancreatic cancer, gastrointestinal cancer, and even in acute leukaemia. Microbial species commonly colonizing head and neck regions seems to be implicated in cancer etiopathogenesis. Understanding the pathogenetic pathways between microbial niches and cancer may represent a promising field of research.