Gastric cancer is second among cancers as a cause of death. More than 90% of all gastric cancers are adenocarcinomas whose principal cause is Helicobacter pylori. Although H. Pylori is a necessary condition, it is not a sufficient condition since only 1-2% of those infected develop gastric cancer. There are multiple factors besides H. Pylori infection involved in the etiology of this cancer. They include genetic factors related to the individual and environmental factors. Although the ways in which H. Pylori participates in this carcinogenesis are not completely clear, two different mechanisms are involved. H. Pylori infection induces persistent inflammation accompanied by hyperproliferation of cells, and it causes damage to DNA from free radicals in which progenitor cells from the bone marrow participate. These cells could be the "stem cells" of gastric cancer. The second path involves the direct action of proteins from H. Pylori on gastric cells. Among the genetic factors involved there is evidence that IL-1B, TNF, IL-8, and INF gama e IL-10 polymorphisms, among others, induce strong inflammatory responses which are associated with higher risks of gastric cancer. [ABSTRACT FROM AUTHOR]