t(14;18)(q32;q21) involving IGH and MALT1 is uncommon in cutaneous MALT lymphomas and primary cutaneous diffuse large B-cell lymphomas

Background: t(14;18)(q32;q21) involving IGH and MALT1 has been demonstrated in cutaneous MALT lymphomas and in one case of primary cutaneous diffuse large B-cell lymphoma (DLBCL). However, the incidence of IGH/MALT1 translocations in these forms of cutaneous lymphoma remains unclear. Methods: We performed paraffin section interphase fluorescence in situ hybridization (FISH) analysis using MALT1 and IGH break-apart probes on 16 cutaneous MALT lymphomas and 16 primary cutaneous DLBCL in order to assess the frequency of IGH/MALT1 translocations and to screen for other potential translocations involving the IGH or MALT1 loci. Results: Translocations involving MALT1 were not detected in any of 16 cutaneous MALT lymphomas or 16 primary cutaneous DLBCL. Of the 12 MALT lymphomas that could be analyzed for an IGH translocation, all were negative. In contrast, four of the 13 cases (31%) of primary cutaneous DLBCL that could be analyzed for translocations involving IGH were positive. Subsequent FISH analysis demonstrated one of these to be an IGH/BCL2 translocation and one to be a CMYC/IGH translocation, while the translocation partners in the remaining two cases are currently unidentified. Conclusions: This study demonstrates that translocations involving MALT1, including IGH/MALT1, are uncommon in cutaneous MALT lymphomas and primary cutaneous DLBCL. Other translocations involving IGH also are not involved in the pathogenesis of at least most cutaneous MALT lymphomas. In contrast, primary cutaneous DLBCL may contain one of several IGH translocations in a minority of cases.