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Introduction

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Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT) designates a group of closely related lymphomas that probably arise in marginal zone/memory B cells [1-6]. Similar lymphomas arise 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. Responsible antigens may be autoantigens or foreign antigens resulting from infection, e.g. Helicobacter pylori infection in gastric MALT lymphoma, Borrelia burgdorferi infection in cutaneous MALT lymphoma and Chlamydia psittaci in ocular adnexal MALT lymphoma. In some but not all countries an association with hepatitis C infection is found. Immunoproliferative small intestinal disease (IPSID), often with synthesis of α immunoglobulin heavy chains, is the result of small intestinal MALT lymphoma.

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Clinical features

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Clinical presentation is dependent on the organ that is involved. Typically, presentation is with gastrointestinal symptoms.

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Haematological and pathological features

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Infiltration is in the marginal zone of reactive follicles associated with mucous membranes, outside a preserved mantle zone. Follicular colonization sometimes occurs. The infiltrate is often closely related to a mucous membrane, which may be invaded (lymphoepithelial lesions) (Figures 9.1, 9.2, 9.3). Lymphoma cells are pleomorphic, 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.

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Figure 9.1

Gastric biopsy from a patient with extranodal marginal zone lymphoma of MALT type. H&E, x 4 objective.

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Figure 9.2

Gastric biopsy from a patient with extranodal marginal zone lymphoma of MALT type, showing lymphoepithelial lesions. H&E, x 20 objective.

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Figure 9.3

Gastric biopsy from a patient with extranodal marginal zone lymphoma of MALT type, showing lymphoepithelial lesions. H&E, x 60 objective.

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The peripheral blood and bone marrow are often normal, although bone marrow infiltration is sometimes observed and rarely there are circulating lymphoma cells. Bone marrow infiltration can be nodular or paratrabecular.

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Detailed investigation shows that disease is disseminated at presentation in a third of patients [7].

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Immunophenotype

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Neoplastic cells express weak monotypic immunoglobulin, most often IgM but in the case of IPSID, α chain only. There is expression of B-cell-associated antigens such as CD20, CD22, CD79a and CD79b. Lymphoma cells do not usually express CD5, CD23, FMC7 or cyclin D1. CD11c is sometimes expressed. BCL2 is expressed and BCL6 is not.

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Cytogenetic and molecular genetic ...

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