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Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) designates a group of closely related lymphomas that arise in post-germinal centre marginal zone/memory B cells [1–6]. MALT lymphomas arise in a background of chronic inflammation due to a persistent infection or autoimmune disease. MALT lymphomas are also seen in non-mucosal sites, particularly when there is a lymphoid infiltrate as a result of an autoimmune disease (e.g. Sjögren’s syndrome or Hashimoto’s thyroiditis). Antigenic stimulation appears to be important in the aetiology of MALT lymphomas and ongoing antigenic stimulation may continue to drive the lymphoma, which may not be fully autonomous. Various responsible foreign antigens resulting from infection have been identified such as Helicobacter pylori infection in gastric MALT lymphoma, Borrelia burgdorferi infection in cutaneous MALT lymphoma and Chlamydophila (previously Chlamydia) psittaci in ocular adnexal MALT lymphoma, Achromobacter xylosoxidans in pulmonary MALT lymphoma and Campylobacter jejuni in immunoproliferative small intestinal disease (IPSID). The association with infective agents may vary with geographic location. In some but not all countries, an association with hepatitis C infection is found in a proportion of cases. IPSID, also known as alpha heavy chain disease is a particular type of MALT lymphoma occurring in the small intestine.

Clinical features

MALT lymphomas may arise in almost any anatomical site, the most frequent being gastrointestinal, eye, thyroid, salivary glands, skin and lung. They are generally not encountered in the terminal ileum. Multiple sites may be involved in the same patient. It affects adults with a female predominance in some subtypes particularly in association with autoimmunity. Patients usually present with localized stage IE or IIE disease and less often with systemic disease. Clinical presentation is dependent on the organ that is involved [7,8].

Haematological and pathological features

Infiltration is in the marginal zone around reactive follicles, outside a preserved mantle zone. Follicular colonization frequently occurs and the germinal centres and mantle may be obliterated by the neoplastic cells. The infiltrate is often closely related to epithelial mucosal structures (where present) with infiltration of these structures by neoplastic cells and associated distortion/destruction (lymphoepithelial lesions) (Figures 9.1, 9.2, 9.3, 9.4). Lymphoma cells show variable morphology with cells sometimes described as centrocyte-like and sometimes as monocytoid; they are small or medium sized and the latter have abundant pale cytoplasm. Plasmacytic differentiation is common and sometimes very prominent raising the differential diagnosis with extramedullary plasmacytoma. Scattered large transformed cells are present in the infiltrate but are not seen in large clusters of sheets.

Figure 9.1

Gastric biopsy from a patient with extranodal marginal zone lymphoma of MALT type. Haematoxylin and eosin (H&E) stain, ×4 objective.

Figure 9.2

Gastric biopsy from a patient with extranodal marginal zone lymphoma of MALT type, showing lymphoepithelial ...

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