Helicobacter pylori as a pathogen and carcinogen.

Although recently recognized as a human pathogen. Helicobacter pylori has probably been present in humans for millenia. It represents the most common chronic infection in humans at the present time. Markedly different outcomes of the infection have been recognized, from asymptomatic mild gastritis to peptic ulcer and to lymphoid and epithelial gastric neoplasia. The factors determining the outcome are poorly understood and probably include bacterial, host and environmental forces. The mechanisms involved in carcinogenesis are probably multiple and include excessive cell replication, depletion of protective epithelial mucins and DNA damage related to misplaced release of oxidative species by leukocytes.