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Mucosal associated lymphoid tumors (MALTs) are classified as marginal zone lymphomas and account for 7-8% of all lymphomas including 50% of primary gastric lymphomas. The stomach is most common site for MALTs, but MALTs can an also occur in the lung (15%), head and neck (15%), ocular adnexae (12%), skin (11%), thyroid (4%) and breast (4%). Marginal zone lymphomas can arise in lymph nodes (indolent course with no cure when disseminated). Marginal zone lymphomas that arise as extranodal tumors (MALTS) are special because: They arise in tissues involved by chronic inflammatory disorders of autoimmune (Sjogrens, and Hashimotos) or infectious (helicobacter) origin. Most MALTS remain localized and dissemination occurs late in the clinical course (30% of cases). In early stages proliferation may be antigen driven (ie. cure helicobacter, cure lymphoma). Resection can be performed for cure and is often associated with long disease free intervals. MATLs can also involve the bone marrow (20% at diagnosis) and lymph nodes (8% at diagnosis) and peripheral blood – PB involvement doesn’t affect prognosis. RARELY an M-component can be seen in blood. (exception is IPSID – aberrant alpha heavy chain). MALTS can transform to DLBL.
HISTOLOGY: marginal zone cells (centrocyte-like): small, atypical cells resembling small cleaved follicular center cells with more cytoplasm. May vary in appearance. May have plasmacytic differentiation. Reactive follicles can be pressent with neoplastic marginal and interfollicular neoplastic cells. In epithileal tissues; marginal zone cells inflitrate the epithelium (lymphoepithelial lesion is central to diagnosis)
MARKERS
1. S-IgM , C-Ig (40% of cases), CD19 , CD20 , CD22 , CD79a
2. CD5-, CD10-
CHROMOSOMES
1. trisomy 3 (60% of cases) and t(11:18) (fusion of the API2 apoptosis inhibitor to a novel gene MLT) (25-50% of cases)
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