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KEY CONCEPTS
Marginal zone lymphoma (MZL) is an indolent B-cell non-Hodgkin lymphoma composed of three subtypes: extranodal (mucosal-associated lymphoid tissue [MALT] lymphoma), splenic, and nodal.
MALT lymphoma, the most common subtype, is composed of gastric and nongastric MALT and is often associated with infectious organisms such as Helicobacter pylori.
Nongastric MALT is often associated with inflammatory conditions such as Sjögren syndrome and Hashimoto thyroiditis.
Translocations well characterized in MALT lymphomas include t(11;18), t(14;18), t(1;14), and t(3;14). No unique recurrent chromosomal abnormalities are noted in nodal MZL. MYD88 L265P mutations (as seen in Waldenström macroglobulinemia) have been identified in 10% to 20% of cases of splenic MZL.
WHO classification restricts small lymphocytic lymphoma (SLL) to tumors involving lymph nodes with the same B-cell immunophenotype as CLL without leukemic involvement and considers SLL to be the nodal or tissue counterpart of chronic lymphocytic leukemia (CLL).
Abnormalities of the p53 or MYC genes correlate with increased risk of histologic transformation (Richter syndrome) and poorer prognosis in CLL/SLL.
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MARGINAL ZONE LYMPHOMA
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Marginal zone lymphoma (MZL) is the second most common B-cell–indolent non-Hodgkin Lymphoma (NHL; <10% of NHL cases in adults). MZL generally presents at a median age of 60 years old, and women have a slightly increased propensity toward MZL developing compared with men.1,2 There are three subtypes of MZL: extranodal MZL of mucosa-associated lymphoid tissue (MALT lymphoma), which represents 7% to 8% of all NHLs; nodal marginal zone lymphoma, which represents approximately 2% of all NHLs; and splenic B-cell marginal zone lymphoma (SMZL), representing less than 1% of all NHLs.3,4 Splenic MZL can be associated with circulating lymphocytes with villous cytoplasmic projections. The entity previously described as splenic lymphoma with villous lymphocytes is, in most cases, SMZL.
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Extranodal Marginal Zone B-Cell Lymphoma
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Patients with MALT lymphoma present with extranodal disease that is often localized (stage I-E or II-E). There may be a history of infection or autoimmune disease, which are conditions that lead to chronic B-cell receptor activation.5 Peripheral lymph node involvement is uncommon in patients with MALT lymphoma. The most common site of involvement is the stomach, but numerous other extranodal locations can be involved, including lung, skin, orbit, salivary glands, other parts of the gastrointestinal tract, thyroid gland, and other rare sites.2 Dissemination occurs in up to 30% of cases, most often in patients with nongastric MALT lymphoma, and dissemination generally occurs to other extranodal sites. In patients with nongastric MALT lymphomas, subclinical gastric involvement is not uncommon. The bone marrow is involved in only 10% to 20% of patients.
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The stomach is the best-studied site of involvement. Patients often present with signs and symptoms suggestive of peptic ulcer disease, such as epigastric pain and dyspepsia. Anemia, weight loss, and gastrointestinal bleeding can be seen in patients with more advanced disease. Helicobacter pylori...