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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 continued...

    Classification of Myelodysplastic Syndromes in Children

    The FAB classification of myelodysplastic syndromes (MDS) was not completely applicable to children.[173,174] Traditionally, MDS classification systems have been divided into several distinct categories based on the presence of the following:[174,175,176,177]

    • Myelodysplasia.
    • Types of cytopenia.
    • Specific chromosomal abnormalities.
    • Percentage of myeloblasts.

    A modified classification schema for MDS and myeloproliferative disorders (MPDs) was published by WHO in 2008 and included subsections that focused on pediatric MDS and MPD.[178] The primary WHO classification includes:

    WHO classification of MDS

    • Refractory cytopenia with unilineage dysplasia:
    • Refractory anemia with ring sideroblasts.
    • Refractory cytopenia with multilineage dysplasia.
    • Refractory anemia with excess blasts.
    • MDS with isolated del (5q).
    • MDS, unclassifiable.
    • Childhood MDS:
      • Provisional entity: Refractory cytopenia of childhood.

        Refractory cytopenia of childhood is noted to be reserved for children with MDS who have less than 2% blasts in their peripheral blood and less than 5% blasts in their bone marrow along with persistent cytopenia(s) and dysplasia. It is also noted in the new WHO classification that refractory cytopenia of childhood, unlike MDS in adults, is usually characterized by bone marrow hypocellularity, making the distinction with aplastic anemia and bone marrow failure syndromes often difficult.

    WHO classification of myelodysplastic/myeloproliferative neoplasms

    • Chronic myelomonocytic leukemia (CMML).
    • Atypical chronic myeloid leukemia, BCR-ABL1 negative (aCML).
    • Juvenile myelomonocytic leukemia (JMML).
    • Myelodysplastic/myeloproliferative neoplasm, unclassifiable.
      • Provisional entity: Refractory anemia with ring sideroblasts and thrombocytosis.

        Refractory anemia with ring sideroblasts and thrombocytosis is notable in that 50% to 60% of cases have JAK2 V617F mutations.[179]

    WHO classification of myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA (4q12), PDGFRB (5q33.2), or FGFR1 (8p11.2)

    • Myeloid and lymphoid neoplasms with PDGFRA rearrangement.
    • Myeloid neoplasms with PDGFRB rearrangement.
    • Myeloid and lymphoid neoplasms with FGFR1 abnormalities.

    The peripheral blood and bone marrow findings for the myelodysplastic syndromes according to the 2008 WHO classification schema [178] are summarized in Table 3.

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