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MALT lymphoma
MALT lymphoma (MALToma) is a form of lymphoma involving the mucosa-associated lymphoid tissue (MALT), frequently of the stomach, but virtually any mucosal site can be afflicted. It is a cancer originating from B cells in the marginal zone of the MALT, and is also called extranodal marginal zone B cell lymphoma.
==Diagnosis and staging==
''MALT lymphoma'' is often multifocal disease in the organ of origin and is frequently macroscopically indistinguishable from other disease processes in the GI tract. Endoscopy is key to diagnosing ''MALT lymphoma'', with multiple biopsies of the visible lesions required, as well as samples of macroscopically normal tissue, termed gastric mapping. Histologically, there is expansion of the marginal zone compartment with development of sheets of neoplastic small lymphoid cells. The morphology of the neoplastic cells is variable with small mature lymphocytes, cells resembling centrocytes (centrocyte like cells), or marginal zone/monocytoid B cells. Plasmacytoid or plasmacytic differentiation is frequent. Lymphoid follicles are ubiquitous to ''MALT lymphoma'' but may be indistinct as they are often overrun or colonized by the neoplastic cells. Large transformed B cells are present scattered among the small cell population. If these large cells are present in clusters or sheets, a diagnosis of associated large B-cell lymphoma should be considered. A characteristic feature of MALT lymphoma is the presence of neoplastic cells within epithelial structures with associated destruction of the glandular architecture to form lymphoepithelial lesions.
''MALT lymphoma'' may be difficult to distinguish from reactive infiltrates, and in some cases, multiple endoscopies are required before a confident diagnosis is reached. The Wotherspoon score, which grades the presence of histological features associated with ''MALT lymphoma'', is useful in expressing confidence in diagnosis at presentation.
Immunohistochemistry can be used to help distinguish ''MALT lymphoma'' from other small B-cell NHLs. B-cell-associated antigens such as CD19, CD20, CD22, and CD79a are usually expressed. In contrast to small lymphocytic lymphoma and MCL, staining for CD5 is usually negative, and these lymphomas can be further distinguished with CD23 (positive in small lymphocytic lymphoma) and CyclinD1 (positive in MCL).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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