Increased Immunohistochemical CD138 Expression in Waldenström's Macroglobulinemia (WM) in Comparison with Splenic Marginal Zone Lymphoma (SMZL).

Abstract 5008 Introduction Differentiating Waldenström's Macroglobulinemia (WM) from other lymphomas and especially Splenic Marginal Zone lymphoma (SMZL), which presents common features with WM, consists a challenge. There is no characteristic molecular abnormality neither for WM nor for SMZL, while in addition, serum IgM cut off is no longer used for the diagnosis of WM. Moreover, while paratrabecular and intrasinusoidal pattern of bone marrow infiltration are described as typical of WM and SMZL respectively, there is often overlap between them. B-lymphocytes' immunophenotype is usually CD5 and CD23 negative in both entities, although deviations from this pattern may be observed; CD38, a marker of lymphocyte activation, theoretically related to lymphoplasmacytic differentiation and adverse prognosis in Chronic Lymphocytic Leukemia, may be expressed. Both WM and SMZL are included among the least reproducible diagnoses of the WHO classification when the diagnosis is based only on clinical grounds, routine laboratory tests and bone marrow biopsy (absence of lymph node or spleen biopsy or typical leukemic picture). CD138 (Syndecan) is expressed in immature as well as in terminally differentiated B-lymphocytes, especially in plasma cells. A strong CD138 expression is observed in myeloma plasma cells. Aim To evaluate firstly whether CD138 is expressed in WM and SMZL and secondly if its expression may help in the differential diagnosis of these entities. Patients and methods 61 patients were studied at presentation, 40 with WM and 21 with SMZL. Among WM patients, 16 were females and 24 males with a median age of 64 years. 57% presented anemia with hemoglobin<12gr/lt, 12% lymphathenopathy and 5% splenomegaly. Among SMZL patients, there were 8 females and 13 males (median age 61 years). 70% presented anemia and 9% lymphathenopathy. In all 61 patients bone marrow was infiltrated by neoplastic cells. By definition, all WM patients had a monoclonal serum IgM paraprotein while 19% of SMZL patients secreted a serum monoclonal paraprotein, either IgM or IgG. Paraffin embedded sections of bone marrow biopsies performed at diagnosis, were stained with anti-CD138 monoclonal antibody, CD138 expression was evaluated in the bone marrow of all patients and comparison between the two patient groups was made. 10% CD 138 expression in bone marrow neoplastic cells was used as cut-off for the evaluation of positivity or negativity. Results 62% of WM patients presented CD138 expression in contrast with 14% of SMZL patients. Median percentage of total CD138 expression in neoplastic cells in WM was 26.5% (range 2-100%) while in SMZL it was 8% (range 0-30%). These differences were statistically significant (p<0.01). It is interesting to note that, 3 out of 4 SMZL patients who secreted IgM at low levels did not express CD138. Otherwise in WM patients CD138 expression correlated only with serum IgM levels. In addition it was observed that 68% of WM patients expressed CD38 by bone marrow lymphocyte flow cytometry compared to 5% of SMZL (p<0.01); however this finding was not related to CD138 immunohistochemical expression. Conclusions Patients with WM presented increased CD138 expression when compared to SMZL patients. If confirmed in larger series, CD138 expression could help differentiating the two entities. Disclosures No relevant conflicts of interest to declare.