Multiparametric Flow Cytometry in Mixed Phenotype Acute Leukemia

Mixed phenotype acute leukaemia (MPAL) is a diverse group of leukemia of ambiguous lineage diagnosed when blasts in peripheral blood and/or bone marrow have antigens of more than one lineage or a mosaic of blasts belonging to more than one lineage. Retrospective analysis of 218 consecutive cases of acute leukaemia diagnosed by multiparametric flow cytometry (FCM) was done. MPAL cases were identified in accordance with European Group for the Immunological Classification of Leukaemias Criteria and World Health Organization 2008/2016 guidelines for lineage assignment. Nine out of 218 (4.1%) cases were classified as MPAL. Eight out of nine patients (88.8%) were male and 4/9 (44.4%) were < 20 years of age. There were three cases of B/T and T/myeloid MPAL each. Two cases were B/myeloid MPAL and one case was chronic myeloid leukaemia (CML) in B/myeloid blast crisis. B/myeloid MPAL and CML in B/myeloid blast crisis cases were Philadelphia chromosome positive. The latter case had a complex karyotype as well. Seven cases were treated with acute lymphoblastic leukaemia treatment regimen; two of them achieved complete remission (CR). The patient with CML in B/myeloid blast crisis was treated with imatinib based regimen, attained CR, underwent allogenic bone marrow stem cell transplantation, but developed graft versus host disease. Five patients died due to complications of febrile neutropenia early in the course of treatment (62.5%). The last patient (B/T MPAL) refused therapy and was lost to follow-up. Early accurate diagnosis of MPAL requires FCM. It may be misdiagnosed if a limited panel of antibodies is used.