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INTRODUCTION

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SUMMARY

Indolent B-cell lymphomas deriving from the marginal zone include three specific entities: extranodal marginal zone (or mucosa-associated lymphoid tissue) lymphoma (EMZL), splenic marginal zone lymphoma (SMZL), and nodal marginal zone lymphoma (NMZL). The clinical and molecular characteristics are distinctive for each of these entities, although some phenotypic and genetic features are overlapping. EMZL is the most common entity, arising at virtually any extranodal site, commonly associated with chronic antigenic stimulation either as a result of an external infection (e.g., Helicobacter pylori in the stomach) or an autoimmune disease (as Sjögren syndrome or Hashimoto thyroiditis). SMZL accounts for approximately 20 percent of all marginal zone lymphomas, with patients typically presenting with an enlarged spleen and involvement of marrow and splenic hilar lymph nodes. NMZL is the least-common entity, representing approximately 10 percent of all marginal zone lymphomas and typically presenting with lymph node-based disease without splenic or extranodal site involvement.

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Acronyms and Abbreviations

AKT1, protein kinase Bα; BCL6, B-cell CLL/lymphoma 6 gene; BCL10, B-cell CLL/lymphoma 10 gene; BCR, B-cell receptor; CD, cluster of differentiation; EMZL, extranodal marginal zone lymphoma; HCV, hepatitis C virus; Ig, immunoglobulin; IGHV, immunoglobulin heavy-chain variable region gene; IPSID, immunoproliferative small intestinal disease; LDH, lactate dehydrogenase; LPL, lymphoplasmacytic lymphoma; MALT, mucosa-associated lymphoid tissue; MZL, marginal zone lymphoma; NF-κB, nuclear factor-kappa B; NMZL, nodal marginal zone lymphoma; PAX5, paired box gene 5; PIM1, protooncogene proteins pim; ROS, reactive oxygen species; SMZL, splenic marginal zone lymphoma; WHO, World Health Organization.

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INTRODUCTION AND CLASSIFICATION

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Marginal zone lymphomas (MZLs) represent a heterogeneous group of indolent lymphoproliferative disorders originating from memory B-lymphocytes, which are normally present in the marginal zone—that is, the outer part of the mantle zone—of the secondary lymphoid follicles. The spleen and the mucosa-associated lymphoid tissues (MALT) are the most frequently involved anatomic compartments; lymph nodes may also been involved, albeit rarely. The 2008 World Health Organization (WHO) Classification of Tumours of Haematopoietic and Lymphoid Tissue identifies three distinct subtypes of MZL based on the involved site, the clinical presentation and course of the disease, as well as the molecular profiles, namely, extranodal MZL of MALT type (also termed extranodal marginal zone lymphoma [EMZL]); splenic marginal zone lymphoma (SMZL); and nodal marginal zone lymphoma (NMZL).1 In addition, two provisional entities are recognized by the 2008 WHO classification: splenic diffuse red pulp lymphoma and hairy-cell leukemia variant, which represent two subtypes of splenic lymphomas with features overlapping with those of MZL.

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In adults, MZLs account for 5 to 17 percent of all non-Hodgkin lymphomas (NHLs); MALT lymphoma is the most frequent overall, being the third most frequent NHL and representing 7 to 8 percent of all B-cell neoplasms. It mostly affects middle-aged adults, at a median age of 60 years, with a slight female preponderance and often in association with chronic antigenic stimulation, either as a consequence of ...

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