Mucosa-associated lymphoid tissue translocation gene 1 (MALT1) is a paracaspase that is a critical mediator of T-cell receptor activation of NF-κB and may contribute to the progression of MALT lymphomas. It contains two immunoglobulin-like domains, an amino-terminal death domain and a carboxy-terminal caspase-like domain. Association of MALT1 with Bcl-10 and CARD11/Carma1 leads to activation of IKK and subsequent stimulation of NF-κB, resulting in increased proliferation and inhibition of apoptosis. A common translocation in MALT B-cell non-Hodgkin lymphomas t(11;18)(q21;q21) results in the fusion of the amino terminus of API2 (c-IAP2), a member of the inhibitor of apoptosis protein family, to the carboxy terminus of MALT1. The API2-MALT1 fusion protein likely leads to deregulation of NF-κB, contributing to increased oncogenic potential.