Splenic marginal zone lymphomas with peripheral CD5 expression.

We report 4 cases of splenic marginal zone lymphoma (SMZL) with peripheral CD5 positive, B-cell lymphocyto-sis. This unusual immunophenotypic discordance raises dilemmas in the diagnostic approach of these patients. In addition, this association may be related to a more aggressive clinical course, as 3 out of 4 of our patients died from progressive disease. Splenic marginal zone lymphoma (SMZL) is a B-cell neo-plasm with an indolent clinical course, characteristic histo-logic pattern of involvement and a non-specific immu-nophenotypic profile. The lymphomatous cells express surface immunoglobulin of IgM and IgD class, are CD19, CD22, CD20, CD79a positive and CD5, CD10, CD23, CD43, cyclin D1 negative. 1,2 This immunophenotype differentiates SMZL from follicular and mantle cell lymphomas (MCL), as well as from B-chronic lymphocytic leukemia (B-CLL). However, the lack of specific immunophenotypic markers for SMZL creates problems for the differential diagnosis of SMZL from immunocytoma/lymphoplasmacytic lymphoma. Moreover, CD5 expression has been reported in histologically typical marginal zone B-cell lymphomas. 3,4 This aberrant CD5 expression has been thought to be a marker for early dissemination and aggressive disease in some patients. 3 We studied four patients with splenomegaly and lym-phocytosis. Peripheral blood smears showed monocytoid B-cells, centrocyte-like cells and varying percentages of villous lymphocytes (Figure 1A). Flow cytometry of the peripheral blood revealed an IgMDκ, CD19 + , bright CD20 + , CD79b + , CD79a + and FMC7 + B-cell population, co-expressing the CD5 molecule in all 4 cases. None of the cases expressed CD23, CD43, CD10, CD103 or cyclin D1. Bone marrow biopsies revealed a lymphomatous infiltration by small lymphocytes, which ranged from 40-70%. In all cases the pattern of distribution was mainly intrasinusoidal combined, to a lesser extent, with interstitial infiltration, a pattern which has been considered suggestive of possible SMZL.