Molecular and Clinicopathologic Significance of Gene Alteration Associated with MALT Lymphoma

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API2-MALT1 fusion gene, cloned from t(11;18)(q21;q21) chromosomal translocation, is a gene abnormality specific to extranodal marginal zone B-cell lymphoma of mucosal-associated lymphoid tissue (MALT). However, the clinicopathologic significance of this chimeric gene remains to be clarified. We have developed a very sensitive multiplex RT-PCR assay for the API2-MALT1 fusion transcript using paraffin materials as a source of RNA, and enabled a large cohort study on this gene abnormality. Our data of a large series of pulmonary MALT lymphoma suggest that the API2-MALT1 fusion may be a causative gene abnormality unrelated to autoimmune disease. In addition, this alteration may define a homogeneous MALT lymphoma subtype that is clinically more indolent and histologically more "typical". Our observation that API2-MALT1 fusion is independence of autoimmune disease is further supported by the data obtained from the study of thymic MALT lymphoma. Aberrant nuclear BCL10 expression may have a possible role as a tool to screen for this API2-MALT1 fusion in pulmonary MALT lymphoma, but this is not the case with cutaneous MALT lymphoma. Case of rare esophageal and ureteral MALT lymphomas have been reported.