Exploring the role of the oral microbiome in saliva, sputum, bronchoalveolar fluid, and lung cancer tumor tissue: A systematic review

Objective

To explore the association between the oral microbiome and the presence or progression of lung cancer (LC) using metagenomic sequencing techniques.

Methods

Databases, including PubMed and EMBASE, were reviewed. Eligible studies included the study of oral microorganisms via genomic sequencing and molecular mechanisms associated with LC in saliva, sputum, bronchoalveolar lavage fluid (BALF), or tumor tissue from LC patients. A quality analysis of the studies was carried out, and a qualitative synthesis was performed according to the localization and sample type. Meta-analysis was performed on alpha diversity indexes.

Results

Of the 1880 scrutinized articles, 50 studies were selected, comprising 29 cross-sectional, 7 case-control, and 14 cohort studies. The quality analysis sheds light on potential biases. The findings revealed a conspicuous overgrowth of specific microbial taxa in LC patients' saliva BALF samples of Veillonella and Streptococcus. Conversely, the Bacteroides genus, related to periodontal disease, exhibited no significant correlation with LC. Microorganisms in tumoral tissue were associated with poor prognosis. Veillonella was associated with a better response to ICIs therapy. Oral microorganisms were related to metabolic reprogramming with xenobiotic biodegradation, amino acid, sugar, sucrose, and lipidic metabolism, immune modulation, and proinflammatory responses.

Conclusion

Overgrowth of specific oral microorganisms in the saliva and BALF is associated with diagnosis, poor prognosis, and low response to immunotherapy. Veillonella could be a marker for response to ICIs therapy. Further well-designed studies should evaluate the impact of the oral microbiome on the response to ICIs.