Pathogenesis and early lesions in extranodal lymphoma.

Extranodal lymphomas that arise in tissues normally devoid of lymphoid tissue provide a unique opportunity for the study of the pathogenesis of lymphoma without the distraction of surrounding lymphoid tissue. This applies particularly to mucosa-associated lymphoid tissue (MALT) B-cell lymphomas, so named because they recapitulate the structure of normal MALT rather than that of lymph nodes. Before these lymphomas develop, MALT accumulates, usually in response to autoimmune injury associated with chronic gastritis caused by Helicobacter pylori, Sjõgren's syndrome, Hashimoto's thyroiditis or other as yet uncharacterized disorders. The factors that induce MALT in these tissues and the point at which a clonal population of B cells arises are currently under investigation. Other extranodal lymphomas that arise in a setting of long prodromata include enteropathy associated T-cell lymphoma (EATL) which occurs in some patients with coeliac disease and lymphomas associated with immunodeficiency that appear to be caused, at least in part, by the Epstein-Barr virus. Application of new, particularly molecular genetic, techniques to the study of these extranodal lymphomas should also provide insight into the aetiopathogenesis of the more common nodal lymphomas.