Mantle cell lymphoma with flow cytometric evidence of clonal plasmacytic differentiation: A case report

Background: Plasmacytic differentiation in mantle cell lymphoma (MCL) occurs rarely. However, no flow cytometric studies that demonstrate plasmacytic (PC) differentiation in MCL have been reported. Herein, we report a case of MCL with PC differentiation identified by flow cytometry. Methods: Morphologic review was performed by hematoxylin and eosin (H&E) stained sections from paraffin-embedded lymph node, colon and bone marrow specimens, and Wright-Geimsa stained bone marrow aspirate smears and touch imprints. Immunohistochemical stains using antibodies against CD3, CD5, CD20, and cyclin-D1, and in-situ hybridization for kappa and lambda light chains were reviewed. Multicolor flow cytometry analysis was performed on the bone marrow aspirate with monoclonal antibodies to CD3, CD4, CD5, CD8, CD14, CD19, CD20, CD23, CD38, CD45, CD56, CD138, and kappa and lambda light chains. FISH analysis for t(11; 14)(q13;q32) was performed on interphase cells. Results: The neoplastic cells had the cytologic features of MCL with nodal, bone marrow, and colonic involvement. In-situ hybridization for kappa and lambda light chains demonstrated clonal plasma cells in the lymph node and bone marrow biopsies. In addition, flow cytometric studies of the bone marrow aspirate showed three populations of neoplastic cells: a clonal B-cell population with typical MCL phenotype, a similar B-cell population in transition to plasma cells, and a clonal plasma cell population. The plasma cells retained CD5 expression and had the same light chain restriction as the clonal B-cells. Conclusions: Multi-parameter flow cytometry can be useful in demonstrating clonal PC differentiation in MCL and distinguishing from a concurrent but unrelated plasma cell dyscrasia.