Recent knowledge of the relationship between Helicobacter pylori and gastric cancer and recent progress of gastroendoscopic diagnosis and treatment for gastric cancer.

Gastric cancer is a multi-step process and multi-factorial disease. However, Helicobacter pylori plays the most important role in gastric carcinogenesis because most gastric cancers including both intestinal type and diffuse type arise from mucosa infected by H. pylori. The relationship between H. pylori infection and gastric cancer has been proved in epidemiological studies, animal experiments with Mongolian gerbils, and clinical prospective studies. Significant preventive effect of H. pylori eradication was reported in Japanese randomized study for secondary gastric cancer after endoscopic resection of primary gastric cancer and meta-analysis of randomized studies. The Japanese Society for Helicobacter Research has published a guideline recommending that H. pylori infection should be treated by eradication therapy to suppress the incidence of gastric cancer. The development of endoscopic technology has advanced the diagnosis and treatment of gastric cancer. In the diagnosis of gastric cancer, image enhancement endoscopy including magnifying observation with narrow-band imaging system and microscopic magnifying observation opens the possibility of optical biopsy. Endoscopic resection for early stage of gastric cancer has been established as proper treatment of early gastric cancer. Recently endoscopic submucosal dissection had made en bloc resection possible for mucosal cancers >2 cm in diameter. Because of endoscopic submucosal dissection, endoscopic resection is indicated in a greater number of cases. Although the use of endoscopic treatment for gastric cancer has been increasing steadily, long-term outcome data is necessary.