[1350] Plasma Cell Myeloma (PCM) with Immunophenotypic Features Transitional between that of Myeloma and Lymphoma

Daisy Alapat, David Viswanatha, Ming Xie, Robert Lorsbach. UAMS, Little Rock; Mayo Clinic, Rochester; William Beaumont Hospital, Royal Oak

Background: PCM has distinctive pathologic features, readily permitting diagnosis in most cases. However, some PCMs share morphologic or immunophenotypic features with lymphoma. Distinction of PCM from lymphoma is critical given the different treatment modalities and the generally poor prognosis associated with PCM. Here we describe 4 cases of PCM morphologic and immunophenotypic features intermediate between those of PCM and low-grade B-cell lymphoma with plasmacytic differentiation (BCL-PC).
Design: Cases were identified during the course of routine clinical practice, and the morphologic, immunophenotypic and cytogenetic features reviewed. Flow cytometry (FC) and/or immunohistochemistry (IHC), and IGH/CCND1 FISH was performed in all cases. A case was considered “transitional” PCM if it manifested immunophenotypic features of PCM and B-cell lymphoma, namely, surface light chain (LC) restriction, CD45 and/or CD20 expression, or coexpression of PAX5 and MUM1/CD138.
Results: Four cases satisfied the above criteria. 2/4 patients had osteolytic lesions and either an IgA or IgG paraprotein. Peripheral blood involvement was present in 1/4 patients. In the bone marrow, all 4 cases had a significant infiltrate of lymphoplasmacytic cells. By FC, a surface kappa LC restricted population of lymphoplasmacytic cells was detected in 4/4 cases, with CD20 expression of variable intensity in 3/4 cases. Expression of CD19 and CD56 was observed in 1/3 analyzed cases, and variable CD45 expression was detected in 2/2 analyzed cases. Notably, 3/3 cases showed coexpression of PAX5 and MUM1/CD138. By IHC, all 4 cases expressed cyclin D1 and contained the IGH/CCND1 fusion by FISH; deletion of chromosome 13q was detected in 1/3 analyzed cases.
Conclusions: PCM may rarely manifest certain morphologic and immunophenotypic features that are intermediate between myeloma and lymphoma. Significantly, all cases contained the t(11;14) and were cyclin D1+. Although previously associated with small-lymphocyte morphology and CD20 expression in PCM, our findings indicate a greater degree of immunophenotypic and morphologic ambiguity in a subset of PCMs with the t(11;14) than has been previously recognized. The diagnostic challenge of such cases is affirmed by the fact that all 4 cases were initially misdiagnosed as BCL-PC. While rare, recognition of PCM with “transitional” immunophenotypic features is important to preclude their misdiagnosis as lymphoma and to insure their appropriate clinical management.
Category: Hematopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 233, Wednesday Afternoon


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