Marginal-zone B-cell lymphoma of extranodal mucosa-associated lymphoid tissue type: molecular genetics provides new insights into pathogenesis.

Marginal zone B-cell lymphoma of extranodal mucosa-associated lymphoid tissue (MALT) type is recognized as a distinct clinicopathologic entity in the revised European-American lymphoma (REAL) and recently published World Health Organization (WHO) classifications. These neoplasms are thought to arise from the extranodal equivalent of the lymph node marginal zone. Two recurrent chromosomal translocations, to date, have been implicated in the pathogenesis of these neoplasms. The t(11;18)(q21;q21), which is far more common, disrupts the api2 gene on chromosome 11q21 and the malt1 (mlt) gene on chromosome 18q21, resulting in the synthesis of a novel fusion gene and protein, API2-MALT1. The t(1;14)(p22;q32), which is uncommon, juxtaposes the bcl-10 gene on chromosome 1p22 adjacent to the immunoglobulin heavy chain (IgH) gene on chromosome 14, wherein BCL10 is overexpressed via the influence of the IgH enhancer. BCL-10 may then form a complex with MALT1 in the cell. Both translocations result in increased inhibition of apoptosis, conferring a survival advantage. Recent work suggests that API2-MALT1 and BCL-10-MALT1 may activate NF-kB and a common downstream signaling pathway.