t(14;18)(q32;q21)-bearing pleural MALT lymphoma with IgM paraproteinemia: value of detection of specific cytogenetic abnormalities in the differential diagnosis of MALT lymphoma and lymphoplasmacytic lymphoma.

A 67-year-old woman presented with a pleural effusion and a tumor in the right pleural wall. Histological examination of thoracoscopic tumor and pleural biopsy specimens showed infiltration by medium sized cells, some of which showed plasmacytoid differentiation. In view of the presence of IgM paraproteinemia and bone marrow involvement by lymphoma cells, the patient was diagnosed tentatively as having lymphoplasmacytic lymphoma (LPL). However, chromosomal analysis of the cells in the pleural fluid detected t(14;18)(q32;q21), while fluorescence in situ hybridization was positive for 11% of the MALT1 split signal. Because of the presence of characteristic genetic abnormalities and notable extranodal involvement, the patient was diagnosed as having MALT lymphoma. She was treated with three courses of cladribine and rituximab, and achieved complete regression of the tumor. In this case the detection of t(14;18)(q32;q21) involving IGH and MALT1 was useful for the differential diagnosis of LPL and MALT lymphoma.