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.aggressive: Sézary disease 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. MALT lymphoma is an 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). Gastric MALT lymphoma is frequently associated (72–98%) with chronic inflammation as a result of the presence of Helicobacter pylori, potentially involving chronic inflammation, or the action of H. pylori virulence factors such as CagA. The initial diagnosis is made by biopsy of suspicious lesions on esophagogastroduodenoscopy (EGD, upper endoscopy). Simultaneous tests for H. pylori are also done to detect the presence of this microbe. In other sites, chronic immune stimulation is also suspected in the pathogenesis (e.g. association between chronic autoimmune diseases such as Sjögren's syndrome and Hashimoto's thyroiditis, and MALT lymphoma of the salivary gland and the thyroid). Due to the causal relationship between H. pylori infection and MALT lymphoma, identification of the infection is imperative. Histological examination of GI biopsies yields a sensitivity of 95% with five biopsies, but these should be from sites uninvolved by lymphoma and the identification of the organism may be compromised by areas of extensive intestinal metaplasia. As proton-pump inhibition can suppress infection, any treatment with this class of drug should be ceased 2 weeks prior to biopsy retrieval. Serology should be performed if histology is negative, to detect suppressed or recently treated infections. Following the recognition of the association of gastric MALT lymphoma with H. pylori infection, it was established that early-stage gastric disease could be cured by H. pylori eradication, which is now the mainstay of therapy. Fifty to 95% of cases achieve complete response (CR) with H. pylori treatment. A t(11;18)(q21;q21) chromosomal translocation, giving rise to an API2-MLT fusion gene, is predictive of poor response to eradication therapy. Radiotherapy is a valid first option for MALT lymphoma. It provides local control and potential cure in localized gastric stage IE and II 1E disease with 5-year EFS of 85-100% reported in retrospective studies. However, the irradiation field is potentially large as it must include the whole stomach, which can vary greatly in size and shape. Irradiation techniques have improved considerably in the last 20 years, including treating the patient in a fasting state, decreasing the irradiated field and required dose. The moderate dose of 30 Gray (Gy) of involved-field radiotherapy administered in 15 fractions (doses) can be associated with tolerable toxicity and excellent outcomes. Hence, radiotherapy is the preferred approach for local disease where antibiotic therapy has failed, or is not indicated. Evidence also suggests that radiotherapy can be utilized to control localized relapses outside the original radiation field.