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Objectives: To examine the utility of CD11c expression on monocytes in normal controls and patients with chronic myelomonocytic leukemia (CMML) (n = 23) with flow cytometric immunophenotyping. Methods: Twenty-three CMML samples and 10 control bone marrows submitted for lymphoma staging without evidence of disease were examined. Results: Monocytes in CMML samples ranged from 4% to 35%. Expression of at least one aberrant monocytic marker was found on the monocytes in 18 (82%) of 22 evaluable cases. The most common aberrancy was underexpression of CD11c (n = 15), while none of the bone marrow controls showed underexpression of CD11c. Conclusions: A distinct heterogeneous population of monocytic cells with underexpression of CD11c was identified in all these cases. CD11c underexpression was independent of other aberrancies, including HLA-DR underexpression (n = 14), aberrant CD56 expression (n = 11), and underexpression of CD33, CD38, and CD14 (n = 6, 5, and 5, respectively), supporting the utility of CD11c expression status on monocytes in establishing a CMML diagnosis. [ABSTRACT FROM AUTHOR]

Objectives: To assess a large series of patients with acute myeloid leukemia (AML) with t(8;21) for both IGH@ and IGK@ B-cell gene rearrangements and for expression of PAX5, OCT2, and Bob.1 by immunohistochemistry and expression of CD19, CD79a, CD20, and CD22 by flow cytometry immunophenotyping. Methods: A total of 48 cases of AML with t(8;21)(q22;q22) were evaluated by immunohistochemistry and/or heavy chain and light chain immunoglobulin rearrangement studies where paraffin-embedded and/or fresh frozen material was available for study; previously performed flow cytometry studies were also reviewed in available cases. Results: Our study yielded 1 of 19 cases of AML with t(8;21) with an IGH@ gene rearrangement; blasts were associated with weak PAX5 expression. In addition, expression of antigens CD79a by flow cytometry and OCT2 by immunohistochemistry were highly associated with PAX5 expression, and CD19 was expressed in most cases assessed. Conclusions: Although B-cell antigen and B-cell transcription factor expression is seen in the majority of AMLs with t(8;21)(q22;q22) and correlates with PAX5 expression, immunoglobulin gene rearrangements are an uncommon event in this group of leukemias. [ABSTRACT FROM AUTHOR]

Objectives: This session of the Society for Hematopathology/European Association for Haematopathology Workshop focused on acute leukemias of ambiguous origin. Methods: We provide an overview of mixed-phenotype acute leukemia (MPAL) as recognized in the current World Health Organization classification and summarize diagnostic criteria for major categories of MPAL: B/myeloid, T/myeloid, B/T, and B/T/myeloid. Results: Most MPAL cases submitted were B/myeloid and T/myeloid MPAL, the most frequent types, but three cases of B/T MPAL were also submitted, and examples of all categories are illustrated. We emphasize that a comprehensive approach to immunophenotyping is required to accurately establish the diagnosis of MPAL. Flow cytometry immunophenotyping using a large panel of antibodies is needed as well as confirmatory immunohistochemical analysis and cytochemistry studies for myeloperoxidase and nonspecific esterase. We discuss technical issues in determining blast lineage and possible pitfalls in MPAL diagnosis. In particular, rare cases of B-acute lymphoblastic leukemia (B-ALL) can express myeloperoxidase but are otherwise consistent with B-ALL and should be treated as such. Last, we review the differential diagnosis between acute undifferentiated leukemia and acute myeloid leukemia with minimal differentiation. Conclusions: There was an agreement that diagnosis of MPAL can be challenging, especially if applied flow cytometry panels are not comprehensive enough. [ABSTRACT FROM AUTHOR]