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Marginal zone B-cell lymphomas comprise three distinct clinicopathologic entities with variable clinical presentations, namely, the extranodal marginal zone lymphomas also known as mucosa-associated lymphatic tissue (MALT) lymphoma, the nodal marginal zone lymphoma, and the splenic marginal zone lymphoma. The extranodal type is the most common, accounting for approximately 7.5 percent of all cases of non-Hodgkin lymphoma.

The marginal zone B cells usually have small- to medium-size, irregular nuclei with dispersed chromatin, and inconspicuous nucleoli, resembling centrocytes and express surface immunoglobulins, pan-B antigens (CD19, CD20, and CD79a) and marginal zone-associated antigens (CD35 and CD21), but lack CD5, CD10, CD23, and cyclin D1 expression. Recurrent karyotype abnormalities have been described. All marginal zone lymphoma types present gains of chromosomes 3 and 18 at a higher frequency in comparison with other B-cell lymphomas. Rearrangements and deletions affecting chromosome 7q are most common in primary splenic lymphoma. In extranodal marginal zone lymphoma, three disparate translocations [t(11;18)(q21;q21), t(1;14)(p22;q32), and t(14;18)(q32;q21)], despite involving different genes, appear to affect the same signalling pathway, resulting in the activation of nuclear factor-kappa B (NF-κB), a transcription factor with a central role in immunity, inflammation, and apoptosis. These translocations are not present in splenic and nodal marginal zone lymphomas. Deletions or mutations of the tumor necrosis factor-α–induced protein 3 gene (TNFAIP3, A20, a negative regulator of the NF-κ B pathway) on chromosome 6q was described in all subtypes of marginal zone lymphoma and are likely to represent another pathogenetic mechanism that can lead to NF-κB activation. The most common site of MALT lymphoma is the stomach, although primary involvement may occur at many other sites, including small intestine, lung, salivary gland, thyroid, skin, and other tissues. Most MALT lymphomas arise at sites normally devoid of lymphoid tissue, often preceded by a chronic inflammatory condition (infections or autoimmune disorders), such as Sjögren syndrome, Hashimoto thyroiditis, or, in the case of gastric MALT lymphoma, infection with Helicobacter pylori. Other infectious agents may have a pathogenetic role (Borrelia burgdorferi in cutaneous localizations, Chlamydophila psittaci in the ocular adnexa, and Campylobacter jejuni in the small intestine). Hepatitis C virus is associated with a subset of nodal and splenic marginal zone lymphomas. Appropriate antibiotic therapy eradicating H. pylori infection can lead to the regression of gastric MALT lymphoma in approximately 75 percent of cases. Patients who do not respond to antibiotic therapy may be considered for involved-field radiotherapy. Chemotherapy and immunotherapy with rituximab can be effective in patients with disseminated disease. Patients with splenic or nodal marginal zone lymphoma and hepatitis C virus infection may achieve a lymphoma remission after treatment of viral infection. Once hepatitis C virus infection is ruled out, most patients with nodal or splenic lymphoma can be managed initially with a wait-and-see policy. When treatment is needed, splenectomy is the treatment of choice for the splenic lymphomas. Chemotherapy may be considered for patient who have contraindication to splenectomy and for those with nodal marginal zone lymphoma. Alkylating agents and purine analogues have been reported ...

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