Mantle cell lymphoma in leukemic phase: characterization of its broad cytologic spectrum with emphasis on the importance of distinction from other chronic lymphoproliferative disorders

Background: Mantle cell lymphoma is a mature, virgin B-cell neoplasm characterized immunologically by a panB+, CD5+, CD23-, cyclin D1+ phenotype and genetically by t(11;14)(q13;q32) with overexpression of the cyclin D1 (bcl-1) gene. It usually presents as advanced stage disease, involving lymph nodes, spleen, bone marrow, and extranodal sites, particularly the gastrointestinal tract. However, frank leukemic presentation with high white cell counts is uncommon and can be difficult to distinguish from other chronic lymphoproliferative disorders. The aim of this study was to characterize the morphologic spectrum of leukemic mantle cell lymphoma.

Methods: During the period July 1994 through October 1998, 14 patients with mantle cell lymphoma in leukemic phase were diagnosed at the Department of Pathology, Queen Elizabeth Hospital, Hong Kong. The diagnosis of mantle cell lymphoma was based on histologic and immunocytochemical findings and was confirmed by cyclin D1 immunoreactivity in all cases. The clinical records and laboratory results were reviewed. Peripheral blood smears, bone marrow, and other tissue biopsies were examined, with particular attention to the cytologic features of the leukemic mantle cells.

Results: Mantle cell lymphoma in leukemic phase showed a very aggressive clinical course. Eight patients died at a mean of 13 months, and only 1 patient was disease free. Morphologically, the leukemic mantle cells exhibited a broad morphologic spectrum, with several cytologic patterns identified: 1) mixed small and medium-sized cells, 2) predominantly medium-sized cells, 3) predominantly large cells, and 4) giant cells. Despite variations in the size and nuclear shape, the leukemic mantle cells could usually be recognized by the nuclear irregularity and clefting, moderately dense but evenly distributed chromatin, small nucleoli, and scant cytoplasm.

Conclusions: Recognition of the characteristic cytologic features of leukemic mantle cells can help to distinguish them from other chronic lymphoproliferative disorders. In contrast to the latter, the clinical course is aggressive and response to conventional chemotherapy is poor.