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    Childhood Acute Myeloid Leukemia/Other Myeloid Malignancies Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Classification of Pediatric Myeloid Malignancies

    Table 2. Acute Leukemias of Ambiguous Lineage According to the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissuesa

    Condition Definition
    NOS = not otherwise specified; WHO = World Health Organization.
    a Béné MC: Biphenotypic, bilineal, ambiguous or mixed lineage: strange leukemias! Haematologica 94 (7): 891-3, 2009.[23]Obtained from Haematologica/the Hematology Journal websitehttp://www.haematologica.org.
    Acute undifferentiated leukemia Acute leukemia that does not express any marker considered specific for either lymphoid or myeloid lineage
    Mixed phenotype acute leukemia with t(9;22)(q34;q11.2);BCR-ABL1 Acute leukemia meeting the diagnostic criteria for mixed phenotype acute leukemia in which the blasts also have the (9;22) translocation or theBCR-ABL1rearrangement
    Mixed phenotype acute leukemia with t(v;11q23);MLLrearranged Acute leukemia meeting the diagnostic criteria for mixed phenotype acute leukemia in which the blasts also have a translocation involving theMLLgene
    Mixed phenotype acute leukemia, B/myeloid, NOS Acute leukemia meeting the diagnostic criteria for assignment to both B and myeloid lineage, in which the blasts lack genetic abnormalities involvingBCR-ABL1orMLL
    Mixed phenotype acute leukemia, T/myeloid, NOS Acute leukemia meeting the diagnostic criteria for assignment to both T and myeloid lineage, in which the blasts lack genetic abnormalities involvingBCR-ABL1orMLL
    Mixed phenotype acute leukemia, B/myeloid, NOS-rare types Acute leukemia meeting the diagnostic criteria for assignment to both B- and T-lineage
    Other ambiguous lineage leukemias Natural killer cell lymphoblastic leukemia/lymphoma

    Leukemias of mixed phenotype comprise the following two groups of patients:

    1. Bilineal leukemias in which there are two distinct populations of cells, usually one lymphoid and one myeloid.
    2. Biphenotypic leukemias in which individual blast cells display features of both lymphoid and myeloid lineage.

    Biphenotypic cases represent the majority of mixed phenotype leukemias.[17] B-myeloid biphenotypic leukemias lacking the TEL-AML1 fusion have a lower rate of complete remission and a significantly worse event-free survival (EFS) compared with patients with B-precursor ALL.[17] Some studies suggest that patients with biphenotypic leukemia may fare better with a lymphoid, as opposed to a myeloid, treatment regimen,[18,19,24] although the optimal treatment for patients remains unclear.

    Cytogenetic Evaluation and Molecular Abnormalities

    Chromosomal analyses of leukemia should be performed on children with AML because chromosomal abnormalities are important diagnostic and prognostic markers.[25,26,27,28,29,30] Clonal chromosomal abnormalities have been identified in the blasts of about 75% of children with AML and are useful in defining subtypes with particular characteristics (e.g., t(8;21), t(15;17), inv(16), 11q23 abnormalities, t(1;22)). Leukemias with the chromosomal abnormalities t(8;21) and inv(16) are called core-binding factor leukemias; core-binding factor (a transcription factor involved in hematopoietic stem cell differentiation) is disrupted by each of these abnormalities.

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