Whole Mouth Fluid Microbiome: A New Frontier in Cancer Research

Purpose of Review: The temporal stability exhibited by the salivary bacteriome and the ease of sample collection compared with fecal samples make saliva/whole mouth fluid (WMF) a promising tool for diagnostic and therapeutic applications in the field of microbiomics. This review summarizes current evidence on the reported association between an altered salivary bacteriome and several human cancers. Recent Findings: While numerous epidemiological studies have highlighted disparities in relative abundances of dominant taxa in the saliva of cancer patients and controls, no specific archetype of dysbiosis has yet been identified in association with any of the cancers studied. Nevertheless, associations between certain oral bacteria detected in WMF, particularly those implicated in the development of periodontitis, such as Fusobacterium nucleatum and Porphyromonas gingivalis, have been reported by many investigators and are speculated to play a key role in the aetiopathogenesis of colorectal cancer and pancreatic cancer, respectively. Streptococcus sanguinis was shown to modify the TNF-α and NF-κB pathways and to upregulate genes associated with EBV lytic activation in Nasopharyngeal carcinoma, thus playing an indirect role. Summary: In recent years, evidence has emerged of an association between altered indigenous microbial dysbiosis and many cancers. With our existing knowledge of genomic alterations in carcinogenesis, deciphering the role of the WMF microbiome may improve and support non-invasive diagnosis and prognosis.