Table 5: Oral bacteria associated with healthy controls in the pancreatic cancer studies.

Cancer	Phylum	Genus/species	Main findings	N	Technology used	Case sample	Control sample	Reference
PC	Fusobacteria	leptotrichia	Higher relative abundance associated with a lower risk of PC	361 incident adenocarcinoma of the pancreas, and 371 matching controls	16S rRNA sequencing	Pre-diagnostic oral mouthwash samples from patients	Pre-diagnostic oral mouthwash samples from controls	Fan et al., 2018 [9]
	Porphyromonas	gingivalis	Higher relative abundance associated with a higher risk of PC
	Aggregatibacter	actinomycetemcomitans
	Bacteroidetes	Porphyromonas	Relative abundance decreased in PC samples compared to non-PC samples	8 pancreatic cancer patients, 22 healthy controls, and 78 diagnosed with other diseases (including other cancer types)	16S rRNA sequencing	Saliva samples from pancreatic cancer patients	Saliva samples from healthy patients and patients with other diseases	Torres et al., 2015 [75]
	Proteobacteria	Neisseria	Relative abundance decreased in PC samples compared to non-PC samples
	Firmicutes	Streptococcus mitis	Relative abundance significantly decreased in PC samples compared to healthy control samples	10 patients, and 10 controls	qPCR	Saliva microflora from patients with pancreatic cancer	Saliva microflora from healthy controls	Farrell et al., 2012 [74]
	Proteobacteria	Neisseria elongata
PDAC	Proteobacteria	Neisseria	Relative abundance significantly decreased in PDAC samples compared to healthy control samples	40 newly diagnosed PDAC, and 58 healthy controls	16S rRNA sequencing	Saliva samples from cancer patients	Saliva samples from healthy controls	Olson et al., 2017 [76]
PHC	Bacteroidetes	Porphyromonas	Relative abundance decreased in PHC samples compared to healthy controls	30 PHC patients, and 25 healthy controls	16S rRNA sequencing	Tongue coating sample from patients	Tongue coating sample from healthy controls	Lu et al., 2019 [77]