Acute leukemias of ambiguous origin.
OBJECTIVE
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.
From the Department of Laboratory Medicine and Pathobiology, University Health Network, University of Toronto, Toronto, Canada, and anna.porwit@uhn.ca.
Anna
A
Porwit
Immunology Laboratory, University Hospital of Nancy-Brabois, Nancy, France.
Marie C
MC
Béné
D000208:Acute Disease; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D006801:Humans; D016130:Immunophenotyping; D007938:Leukemia / Q000175:diagnosis* / Q000276:immunology*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000276:immunology* / Q000473:pathology; D014944:World Health Organization
Acute leukemia; Immunophenotype; Lineage; Lymphoid; Mixed phenotype acute leukemia; Myeloid; Undifferentiated acute leukemia