An unusual case of leukemic mantle cell lymphoma with a blastoid component showing loss of CD5 and aberrant expression of CD10.

Characteristically, mantle cell lymphoma (MCL) expresses surface immunoglobulin (sIg), CD19, CD20, and CD5 and lacks CD10 and CD23. Rare CD5-MCL variants have been described. This report describes a case of leukemic MCL with morphologically and immunophenotypically distinct classic MCL and blastoid-variant MCL (BV-MCL) components. The classic MCL had typical morphologic features and immunophenotype (kappa sIg light chain-restricted and CD5+; CD10- and CD23-). The BV-MCL had larger nuclei and open chromatin; these cells also were kappa sIg light chain-restricted; however, they were CD10+ and CD5-. Fluorescence in situ hybridization studies demonstrated cyclin D1-immunoglobulin heavy chain gene fusion in both components; the bone marrow biopsy cellularity was replaced by CD10+ and cyclin D1+ and CD5-BV-MCL. This case illustrates the phenotypic heterogeneity of MCL and underscores the need for histopathologic correlation and, in some instances, ancillary genetic studies to accurately classify B-cell lymphomas.