Les polypes gastriques: Pathologie et génétique

Gastric polyps are defined endoscopically, as lesions bulging from the gastric mucosa into the lumen. Their histological nature is variable. The main difference lies between non neoplastic and neoplastic lesions. The two most frequent types of non neoplastic polyps are fundic gland polyps and hyperplastic polyps. Fundic gland polyps are the most frequent of all gastric polyps; they are located in the fundic region of the stomach and arise in non diseased mucosa; they may be sporadic or may be associated with distinctive clinical settings (familial adenomatous polyposis or FAP and anti-secretory treatment); in the latter case, they are usually multiple; fundic gland polyps are associated with several types of molecular alterations, depending on their etiology: APC gene is involved in FAP-associated lesions and the gene coding for beta-catenin in sporadic ones; in situ development of neoplastic lesions is possible but exceptional. Hyperplastic polyps may occur all over the stomach and always arise in pathological mucosa, usually during autoimmune gastritis or H. pylori infection; they usually are sporadic; no recurrent molecular alteration has been described; the natural history of hyperplastic polyps is characterized by the risk of in situ development of neoplastic foci or of association with a synchronous gastric adenocarcinoma: large hyperplastic polyps must therefore be resected in totality and the adjacent gastric mucosa must be carefully explored. The other non neoplastic gastric polyps include the so-called hamartomatous polyps, which may be solitary or associated with syndromic polyposes (such as Peutz-Jeghers polyps, juvenile polyps, Cowen syndrome and Cronkhite-Canada syndrome), and the inflammatory polyps (fibroid polyps or Vanek's tumors and xanthomas). Neoplastic lesions account for about 15% of gastric polyps; the most frequent ones are adenomas, solitary or associated with FAP; alterations of the APC gene are frequent; a microsatellite instable phenotype may also be observed; the risk of carcinomatous transformation of gastric adenomas depends on their size, architecture and histological type (intestinal or pyloric). In conclusion, many advances have been made in the description of the histological types of gastric polyps and in the understanding of their molecular mechanisms, but progress in the knowledge of their natural history is necessary to improve the strategies of treatment and follow-up.