Methods for determining whether a tissue sample or an analogue and/or derivative thereof comprises a cell with a chromosome (11:18) translocation associated with malignancies such as mucosa-associated lymphoid tissue (MALT) lymphomas. The invention further provides insight into a novel mechanism of transformation of primary cells. The mechanism involves expression of a fusion proteinaceous molecule comprising at least apoptosis inhibitor 2 (API2) or a functional part, derivative and/or analogue thereof fused to at least one other proteinaceous molecule. The invention also provides a novel nucleic acid sequence and proteinaceous molecule expressed from the sequence termed “MALT-lymphoma associated Translocation (MLT) protein.”