Table 1.

Reported studies limitations.

Author, publication date and country	Reported studies limitations
Chen B (2019), China	Not reported
Vogtmann E (2020), USA	1. Saliva sample collected after cancer diagnosis
	2. Unhealthy controls (benign diseases)
	3. Low power study for rate-specific analysis
	4. Information on oro-dental health was not obtained
Half E (2019), Israel	1. Small sample
Serra N (2018), Canada	Not reported
Olson SH (2017), USA	1. Small sample
	2. One-time collection of oral samples
Di Carlo P (2019), Italy	1. Study at a single center
Mei Q-X (2018), China	1. Small sample
	2. Analysis of bacteria only
Erick R (2019), USA	Not reported
Torres PJ (2015), USA	1. Low power study for rate-specific analysis of Streptococcus
	2. Presence of tumor beyond the primary site (pancreas)
Ren Z (2017), China	1. Stool sample collected after cancer diagnosis
Fan X (2018), USA	1. One-time collection of oral samples
	2. Information on oro-dental health was not obtained
	3. Unrepresentative groups of the general population, low generalization power
Kohi S (2021), USA	1. Study at a single center
	2. Presence of confounding factors in cases and controls
	3. Duodenal fluid sample collected after cancer diagnosis
Saab M (2021), France	1 Unhealthy control (benign diseases) and no literature for comparison
	2. No comparison with tumor microbiota
	3. Possibility of contamination of samples with duodenal bacteria
Sun H (2020), China	Not reported
Wei AL (2020), China	1. Non-inclusion of other pancreatic diseases
	2. Only 16S rRNA sequencing for analysis
	3. Information on oro-dental health was not obtained