The pathological sequence in the development of gastric cancer: I.

Although Helicobacter pylori has been designated a Group 1 carcinogen in humans, a causal role for this organism in the pathogenesis of gastric cancer has yet to be established. Histogenetically, gastric cancers have been classified into two main histological types, diffuse and intestinal, which have differing characteristics and pathogenesis. In diffuse-type cancer, minute signet ring tumours develop de novo in the neck region of glands. Gastritis caused by H. pylori infection does not contribute to the development of gastric cancer in this situation. In intestinal-type gastric cancer, the primary event is not always intestinal metaplasia, and the significance of H. pylori in this condition is not clear. There is evidence that a proportion of adenocarcinoma initially have a gastric-type phenotype, but undergo transformation to the intestinal type as the condition progresses.