[Pathology and pathogenesis of extranodal lymphomas in the gastrointestinal tract].

Primary extranodal lymphomas of the stomach represent a fascinating object of investigation for clinicians and basic scientists. Possibly multifocal clonal populations of lymphocytes develop, which progress to highly malignant lymphomas over many years, starting from a previous reactive disease, commonly an Helicobacter-pylori-associated chronic gastritis or an organ related autoimmune disease in case of other sites of MALT lymphomas. In early stages of clonally restrained NHL of low malignancy of the MALT type a complete tumor regression can be achieved by elimination of the triggering agent Helicobacter pylori. At least a long standing remission is expected. The site and the frequency of relapse cannot be predicted until now. Basic requirement for the treatment by eradication of Helicobacter is the doubtless and well documented diagnosis of a low malignant NHL, based on immunohistological++ and molecular biologic findings, to prove scientifically the efficacy of this treatment. This will establish the basis to assess the stage and the grade of a primary gastric lymphoma in the future.