The t(2;5)(p23;q35) translocation results in the formation of a unique chimeric NPM-ALK protein (p80). Expression of this protein is considered to be one of the clinical features of anaplastic large cell lymphoma (ALCL). Recently recognized as one clinical subtype of ALCL, the small cell variant is prone to have a leukemic presentation. Although the small cell variant has been recognized as a subtype of ALCL, the clinical properties of this subtype, especially the immunophenotype of lymphoma cells in peripheral blood, have not yet been fully described. This report shows that neither CD30 nor p80 is detected by immunostaining in the predominant small cell malignant clone and also in large lymphoma cells in peripheral blood, while large cells and occasionally observed small cells in bone marrow were found to be positive for CD30 and p80. Our findings suggest that differential expression of CD30 and p80 between peripheral blood and bone marrow lymphoma cells is a property of the small cell variant of ALCL.
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