MALT lymphoma: Genetic abnormalities, immunological stimulation and molecular mechanism.

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) occurs at diverse anatomic sites and is closely associated with several distinct chronic inflammatory disorders. Both the acquired genetic abnormalities and active chronic immunological responses play a critical role in the development of MALT lymphoma, interestingly by dysregulating similar molecular mechanisms. The three translocations seen in MALT lymphoma, namely t(14;18)(q32;q21)/IGH-MALT1, t(1;14)(p22;q32)/BCL10-IGH, and t(11;18)(q21;q21)/BIRC3 (API2)-MALT1 are capable of activating both canonical and non-canonical NF-κB pathways. TNFAIP3 (A20) inactivation by deletion and/or mutation abolishes its negative regulation to several signalling including BCR and TLR, which activate the canonical NF-κB pathway. Similarly, the immunological responses also activate the canonical NF-κB pathway via surface antigen receptor and TLR, and the non-canonical NF-κB pathway by T-cell help and BAFFR. There is also emerging evidence indicating oncogenic cooperation between the above genetic changes and immunological stimulation in the pathogenesis of MALT lymphoma.