Atypical lymphocytic leukemia and mantle cell lymphoma immunologically very close: flow cytometric distinction by the use of CD20 and CD54 expression

Integration of morphological and immunophenotypic data is critical in achie ving diagnosis accuracy and minimising interobserver interpretative discrep ancies. The aim of this work was to compare the immunophenotype and the mor phology of chronic lymphocytic leukaemia and mantle cell lymphoma, to help in the differential diagnosis of CD5 positive monoclonal B cells. Frozen/th awed samples from 91 patients were analysed retrospectively. Fresh samples from 17 mixed/atypical CLL and 13 MCL were tested to corroborate the result s. Markers were analysed as percentage (%) of positive B lymphocyte subpopu lation, and in terms of median fluorescence intensity (MFI). Matutes's CLL score clearly allowed distinguishing between classical CLL on the one hand, and atypical CLL and MCL on the other hand. The percentage of CD54-positiv e cells and the median fluorescence intensity of CD20 and CD54 were the onl y parameters which were significantly higher in MCL than in atypical CLL (P <0.05), allowing an immunological distinction between these two entities. N evertheless, due to a quenching problem when using CD20 and CD54 together, and because CD18 showed a statistically different expression between classi cal and atypical CLL, the combination of CD18/CD54 has been preferred and s howed a different pattern in the three entities. Immunophenotyping could be helpful in the differential diagnosis of CD5-positive B cell chronic lymph oproliferative disorders with atypical features that do not fit exactly int o any of the morphologic proposed groups.