A possible new morphological variant of mantle cell lymphoma with plasma-cell type Castleman disease-like features.

Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma characterized by overexpression of cyclin D1 resulting from t(11;14)(q13;q32) translocation. Herein, we report 3 cases of MCL with features of plasma cell-type Castleman disease (CD). The 3 patients were all men, ranging from 51 to 74 years in age, and they all presented with systemic lymphadenopathy with anemia, hypoalbuminemia, elevated serum levels of C-reactive protein, and polyclonal hypergammaglobulinemia. Lymph node biopsy specimens of the 3 cases showed histological features of plasma cell-type CD, including atrophic germinal centers and interfollicular plasmacytosis, with no light chain restriction. However, flow cytometric analysis demonstrated an abnormal B-cell population with CD5 expression, and further analysis using cyclin D1 immunostaining highlighted a neoplastic component that was restricted to the mantle zone. These neoplastic cells were immunohistochemically positive for CD20, CD5, and SOX11, and negative for CD3, CD10, and HHV8. The Ki67 index was low. All patients were finally diagnosed with MCL. This rare type of MCL can be misdiagnosed clinically and histologically as CD. Therefore, it is important to recognize this rare type of MCL, and careful examination is required using both histological and flow cytometric analyses.