Cytogenetic and FISH analyses of patients with t(14;18)(q32;q21). (A) FISH study using flanking probes for MALT1 gene in peripheral blood cells from case 2. PACs 119K17 and 83A16 centromeric to MALT1 locus are shown in red; PACs 59N7 and 628B12, telomeric to MALT1 are shown in green. The pooled telomeric probes (green) hybridized to the derivative chromosome 14, whereas the pooled centromeric probes (red) hybridized to the derivative 18. A partial karyotype from case 1 including the t(14;18)(q32;q21) and the trisomy of chromosome 3 is shown in the top left corner. (B) In the SSK-41 cell line, selective amplification of MALT1 but not of BCL2 was observed. Cytogenetic analysis showed der(18)trp(18)(q11q21), which is marked with an arrow, as well as several insertions of chromosome material from 18q21 in different chromosomes. FISH analysis showed amplification of PAC 119K19 flanking 5′ region of MALT1 gene locus but not of PAC 59N7 located 3′ of MALT1, indicating that a chromosome break occurred before amplification. (C) Genomic amplification of MALT1 gene in KHM-10B cell line using MALT1 flanking probes. Eight copies of MALT1 were detected, confirming the array CGH data. (D) Genomic amplification of MALT1 in one case of gastric MALT lymphoma with bulky retroperitoneal disease at diagnosis. Five copies of MALT1 were seen.