CD5 expression identifies a subset of splenic marginal zone lymphomas with higher lymphocytosis: a clinico-pathological, cytogenetic and molecular study of 24 cases

Abstract

Background: Classically, splenic marginal zone B-cell lymphoma is characterized by the absence of CD5 expression. Cases of apparent splenic marginal zone B-cell lymphoma showing CD5 expression, as diagnosed by blood studies, have been described; however, in the absence of histological evidence, the correct diagnosis of these cases is controversial because of possible confusion with other CD5-positive small B-cell neoplasms.

Design and methods: We report a series of 24 CD5-positive, t(11;14)-negative cases of splenic marginal zone B-cell lymphoma diagnosed by flow cytometry studies of blood and histologically proven on spleen sections. Clinical data as well as morphological, immunological, cytogenetic and molecular characteristics were assessed to evaluate the similarities and differences of these cases with those of classical CD5-negative splenic marginal zone B-cell lymphoma.

Results: The CD5 expression detected in blood by flow cytometry was confirmed in most cases by immunohistochemistry on spleen sections. In general, cases of CD5-positive and CD5-negative splenic marginal zone B-cell lymphoma did not appear different and, in particular, they showed similar karyotypic changes such as 7q deletion, trisomy 3, trisomy 18 and biased IGHV usage (i.e. VH1-2). The main differences were a higher lymphocyte count at diagnosis (8.15x10(9)/L versus 3.90x10(9)/L; P=0.005) and more frequent diffuse bone marrow infiltration (34% versus 8%; P=0.03) in the CD5-positive group. A tendency to a more mutated IGHV status in the CD5 positive cases was observed (80% versus 54.5%; (P=0.11). No significant differences in outcome were found in relation to CD5 expression.

Conclusions: This study confirms the existence of cases of CD5-positive splenic marginal zone B-cell lymphoma and shows that these cases are closely related to classical splenic marginal zone lymphoma. Whether or not CD5-positive splenic marginal zone B-cell lymphoma constitutes a true subset obviously requires the study of more cases.

Figure 1.

Cytology of the blood smears from CD5-positive SMZL patients (MGG staining). Tumor cells presented some degree of heterogeneity with a majority of small lymphoid cells with compact chromatin, which is rarely densely-packed in small irregular clumps (a), frequent lymphoplasmocytoid cells (b), villoid lymphocytes with short villi (c) and centrocytic-like cells (d1,d2,d3), rare true villous lymphocytes (e). Medium-sized lymphoid cells with a relatively abundant pale cytoplasm (resembling monocytoid cells)(f1,f2) and plasmacytic cells (g) were uncommon.

Figure 2.

Morphology of spleen sections from patients with CD5-positive SMZL with a classic marginal-zone pattern (A) Hematoxylin eosin safran staining, low magnification (x4) and with strong CD5 immunostaining (B).