Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma)
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50% of all cases of MALT lymphoma occur in the gastrointestinal tract. Within the GI tract, the stomach is the most common primary site. Other sites of involvement include salivary gland, lung, head and neck, ocular adnexa, skin, thyroid, and breast. The majority of patients present with stage I or II disease. A minority have bone marrow (BM) involvement. The frequency of BM involvement is lower in gastric cases and higher in MALT lymphomas arising in the lung and occular adnexa. Multiple extranodal sites may be involved in up to 25% of extragastric cases at the time of presentation. MALT lymphomas may have involvement of multiple extranodal sites, particularly of paired organs (e.g. salivary glands) or organ systems (e.g. gastrointestinal tract, skin). The differential diagnosis includes the history of reactive inflammatory process that typically precedes the lymphoma including: Heliobacter pylori, gastritis, lymphoepithelial sialadenitis, Hashimoto thyroiditis, and other small B-cell lymphomas (follicular lymphoma, mantle cell lymphoma, small lymphocytic lymphoma). The demonstration of immunoglobulin light chain restriction is important in the differential diagnosis.
There are three variants of MALT: IPSID, nodal marginal zone lymphoma, and pediatric nodal marginal zone lymphomas. All are coded to 9699/3.
IPSID is the abbreviation for immunoproliferative small intestinal disease. This variant was recently added to the growing list of infectious pathogen-associated human lymphomas. IPSID involves mainly the proximal small intestine. Geographically, IPSID is most prevalent in the Middle East and Africa.
Nodal marginal zone lymphoma (NMZL) usually presents with involvement of peripheral lymph nodes. Occasionally the bone marrow and peripheral blood are involved. NMZL is a primary B-cell neoplasm that morphologically resembles lymph nodes involved by marginal zone lymphoma of extranodal or splenic types, but without evidence of extranodal or splenic disease. The prognosis for pediatric NMZL is excellent with very low relapse rates and long survival after conservative treatment.
Pediatric nodal marginal zone lymphoma in the pediatric age group has distinct clinical and morphological characteristics. It presents predominantly in males and with localized (90% are Stage I) disease, mainly in the head and neck lymph nodes. Studies for clonal rearrangements of IGH@chain are necessary to help distinguish pediatric NMZL from reactive conditions.