title: Helicobacter pylori and gastric cancer.
abstract: OBJECTIVE
  Although chronic Helicobacter pylori infection is the strongest known risk factor for development of gastric adenocarcinoma, only a small proportion of infected individuals will ever develop tumours. This article discusses various bacterial, host and environmental factors which may influence an individual's susceptibility.
  
  
  RESULTS
  Recent research on bacterial virulence factors has focussed upon the cag pathogenicity island, particularly its roles in regulating epithelial growth and adhesion. Studies of host genetic factors have included several analyses of polymorphisms in inflammatory cytokines in human cohorts. Animal studies have recently clarified the roles of dysregulated epithelial apoptosis, proliferation and differentiation pathways during gastric carcinogenesis, and novel experiments involving H. felis infection of bone marrow transplanted irradiated mice have suggested that gastric cancer may originate from bone marrow-derived stem cells. Important roles for signalling between epithelial and mesenchymal cells, particularly myofibroblasts, are also emerging. Recent research on the importance of environmental factors has demonstrated how helminth coinfection may protect against atrophic gastritis and T helper type 1 responses.
  
  
  CONCLUSIONS
  Complex interactions between several bacterial, host genetic and environmental factors determine whether H. pylori infected individuals develop gastric carcinoma. The importance of bone marrow stem cell engraftment during human gastric neoplasia is an area requiring urgent investigation.
authors.affiliation: Division of Gastroenterology, University of Liverpool, Liverpool, UK. dmpritch@liv.ac.uk
authors.forename: D Mark
authors.initials: DM
authors.lastname: Pritchard
authors.forename: Jean E
authors.initials: JE
authors.lastname: Crabtree
mesh_terms: D000818:Animals; D016481:Helicobacter Infections / Q000150:complications* / Q000382:microbiology; D016480:Helicobacter pylori / Q000472:pathogenicity*; D006801:Humans; D012307:Risk Factors; D013274:Stomach Neoplasms / Q000209:etiology*