Oral and Pancreatobiliary Microbiota in Cancer: A Systematic Review of Compositional Alterations and Their Clinical Implications.

BACKGROUND

Associations between microbial dysbiosis and malignancies of the pancreatobiliary system have been described in recent studies. As a result of the limited number of studies that have been done specifically on the malignancies of the biliary tract, information regarding oral, biliary and tumour-related microbial alterations was combined to provide an overview of the microbial changes that may occur.

METHODS

Studies that involved observations on the composition or presence of dysbiosis of the microbiota from oral (saliva, oral rinse, dental plaque) or other non-oral specimens (bile, pancreatic tissue, duodenal tissue and bacteria-derived extracellular vesicles from plasma) in patients with pancreatobiliary malignancies were considered. The risk of bias was evaluated using the Newcastle-Ottawa Scale (NOS) for case-control study designs and the JBI Checklist for cross-sectional studies.

RESULTS

There were a total of 16 studies involving 1426 participants that were conducted using both case-control and cross-sectional study designs. Samples were collected from saliva, oral wash, bile, pancreatic and duodenal tissues and bacterial extracellular vesicles isolated from plasma samples. The most common method used was 16S rRNA sequencing, and two used shotgun metagenomics. In all the studies, patients with pancreatobiliary cancers, especially PDAC, had a significantly higher abundance of opportunistic microbes like Streptococcus, Veillonella, Fusobacterium, Prevotella and a lower abundance of commensal bacteria like Neisseria and Corynebacterium. There was overlap of microbial profile in the oral cavity and tumour/bile compartments in a few studies.

CONCLUSIONS

Although the current data is preliminary and observational in nature, there are consistent findings linking microbiota dysbiosis with cancers of the pancreatobiliary region within both oral and non-oral body sites. Causality has not been established yet. The use of microbial signatures as a basis for biomarker development is a promising research direction.