Gastric microbiota and carcinogenesis: the role of non-Helicobacter pylori bacteria - A systematic review.
OBJECTIVE
Helicobacter pylori is the strongest risk factor for gastric cancer. However, recent advances in DNA sequencing technology have revealed a complex microbial community in the stomach that could also contribute to the development of gastric cancer. The aim of this study was to present recent scientific evidence regarding the role of non-Helicobacter pylori bacteria in gastric carcinogenesis.


METHODS
A systematic review of original articles published in PubMed in the last ten years related to gastric microbiota and gastric cancer in humans was performed.


RESULTS
Thirteen original articles were included. The constitution of gastric microbiota appears to be significantly affected by gastric cancer and premalignant lesions. In fact, differences in gastric microbiota have been documented, depending on Helicobacter pylori status and gastric conditions, such as non-atrophic gastritis, intestinal metaplasia and cancer. Gastric carcinogenesis can be associated with an increase in many bacteria (such as Lactobacillus coleohominis, Klebsiella pneumoniae or Acinetobacter baumannii) as well as decrease in others (such as Porphyromonas spp, Neisseria spp, Prevotella pallens or Streptococcus sinensis). However, there is no conclusive data that confirms if these changes in microbiota are a cause or consequence of the process of carcinogenesis.


CONCLUSIONS
Even though there is limited evidence in humans, microbiota differences between normal individuals, pre-malignant lesions and gastric cancer could suggest a progressive shift in the constitution of gastric microbiota in carcinogenesis, possibly resulting from a complex cross-talk between gastric microbiota and Helicobacter pylori. However, further studies are needed to elucidate the specific role (if any) of different microorganisms.
CINTESIS, Faculty of Medicine, University of Porto, Portugal.
Emanuel
E
Dias-Jácome
Gastroenterology Department, Oncology Portuguese Institute of Porto, Portugal.
Diogo
D
Libânio
Physiology and Cardiothoracic Surgery, Faculty of Medicine, University of Porto, Portugal.
Marta
M
Borges-Canha
Pathology Department, Oncology Portuguese Institute of Porto, Portugal.
Ana
A
Galaghar
CINTESIS, Faculty of Medicine, University of Porto, Portugal.
Pedro
P
Pimentel-Nunes
D000818:Animals; D063646:Carcinogenesis; D005770:Gastrointestinal Neoplasms / Q000209:etiology / Q000382:microbiology*; D016481:Helicobacter Infections; D016480:Helicobacter pylori; D006801:Humans; D064307:Microbiota; D013274:Stomach Neoplasms / Q000209:etiology / Q000382:microbiology*