Table 1.

List of studies investigating the correlation between oral microbiota alterations and pancreatic ductal adenocarcinoma (PDAC). Pancreatic ductal adenocarcinoma (PDAC); number of subjects (N); healthy control (HC); chronic pancreatitis (CP); intraductal papillary mucinous neoplasm (IPMN); Human Oral Microbe Identification Microarray (HOMIM); the area under the parasitemia curve (AUC).

Ref.	Study Design	N. PDAC Patients	N. Controls	Detection Method	Microbiota Association	Main Findings/Authors’ Conclusion
Farrell et al., 2012 [32]	Case-control	38	38 HC 27 CP	Saliva, 16S rRNA amplicon hybridized on HOMIM array	Granulicatella adiacens increased, Neisseria elongata and Streptococcus mitis decreased abundance in PDAC cases	Combination of salivary N. elongata and S. mitis abundance distinguished cancer patients from healthy controls (AUC = 0.90) and proposed as a specific biomarker for PDAC. G. adiacens and S. mitis distinguished cancer patients from chronic pancreatitis (AUC = 0.68).
Torres et al., 2015 [33]	Case-control	8	22 HC	Saliva, 16S rRNA V3-V4 amplicon sequencing	Leptotrichia and Porphyromonas increased abundance Neisseria and Aggregatibacter decreased abundance in PDAC	Overall microbiota diversity of the groups was very similar. Salivary Leptotrichia to Porphyromonas ratio proposed as PDAC biomarker.
Olson et al., 2017 [34]	Case-control	40	58 HC 39 IPMN	Saliva, 16S rRNA V4–V5 amplicon sequencing	Increased abundance of Firmicutes and related taxa in PDAC versus higher levels of Proteobacteria and related taxa in healthy controls	No differences in overall saliva microbiota diversity (alpha diversity) between PDAC and IPMN patients.
Lu et al., 2019 [35]	Case-control	30	25 HC	Tongue swab, 16S rRNA V3–V4 amplicon sequencing	Fusobacterium, Leptotrichia, Actinomyces, Corynebacterium, Rothia, Moraxella and Atopobium preponderance in PDAC	Haemophilus, Porphyromonas, Leptotrichia and Fusobacterium could distinguish PDAC patients from healthy subjects (AUC = 0.802).
Vogtmann et al., 2020 [36]	Case-control	273	285 HC	Saliva, 16S rRNA V4 amplicon sequencing	Increased abundance of Enterobacteriaceae, Lachnospiraceae G7, Bacteroidaceae or Staphylococcaceae and decreased abundance of Haemophilus associated with PDAC	No differences in overall saliva microbiota diversity (alpha diversity) between PDAC and HC. Significant association between PDAC and microbial community composition (beta diversity).
Michaud et al., 2013 [37]	Prospectivenested case-control	405	410 HC	Plasma (blood) samples, ELISA	Porphyromonas gingivalis ATCC 53978 increased IgG in PDAC	Individuals with high levels of antibodies to P. gingivalis ATCC 53978 are at a 2-fold higher risk of developing PDAC.
Fan et al., 2018 [38]	Prospectivenested case-control study	361	371 HC	Mouthwash, 16S rRNA V3-V4 amplicon sequencing	P. gingivalis and A. actinomycetemcomitans increased abundance	P. gingivalis and A. actinomycetemcomitans were associated with a higher risk of PDAC, while Fusobacteria and Leptotrichia were associated with a decreased risk.