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    Adult Acute Myeloid Leukemia Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Classification of Adult Acute Myeloid Leukemia

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    Acute erythroid leukemias (FAB classifications M6a and M6b)

    The two subtypes of the acute erythroid leukemias, erythroleukemia and pure erythroid leukemia, are characterized by a predominant erythroid population and, in the case of erythroleukemia, the presence of a significant myeloid component. Erythroleukemia (erythroid/myeloid; M6a) is predominantly a disease of adults, comprising approximately 5% to 6% of cases of AML.[63] Pure erythroid leukemia (M6b) is rare and occurs in all age groups. Occasional cases of chronic myeloid leukemia (CML) may evolve to one of the acute erythroid leukemias.[57] Erythroleukemia may present de novo or evolve from an MDS, either RAEB or RCMD-RS or RCMD. (Refer to the PDQ summary on Myelodysplastic Syndromes Treatment for more information.) The clinical features of these acute leukemias include profound anemia and normoblastemia. (Refer to the PDQ summary on Fatigue for more information.)

    Morphologic and cytochemical features of erythroleukemia include the following:[57]

    • 50% or more erythroid precursors in the entire nucleated cell population of the bone marrow.
    • 20% or more myeloblasts in the nonerythroid population in the bone marrow.
    • Dysplastic erythroid precursors with megaloblastoid nuclei.
    • Multinucleated erythroid cells.
    • Myeloblasts of medium size, occasionally with Auer rods.
    • Ringed sideroblasts.
    • Positive PAS stain in the erythroid precursors.
    • Hypercellular bone marrow.
    • Megakaryocytic dysplasia.

    Morphologic and cytochemical features of pure erythroid leukemia include the following:

    • Medium- to large-sized erythroblasts with round nuclei, fine chromatin, one or more nucleoli, deeply basophilic cytoplasm, and occasional coalescent vacuoles.
    • Erythroblasts reactive with alpha-naphthyl acetate esterase.
    • Acid phosphatase.
    • PAS.

    Immunophenotyping in erythroleukemia reveals erythroblasts that react with antibodies to glycophorin A and hemoglobin A and myeloblasts that express a variety of myeloid-associated antigens (CD13, CD33, CD117, c-kit, and MPO). Immunophenotyping in acute erythroid leukemia reveals expression of glycophorin A and hemoglobin A in differentiated forms. Markers such as carbonic anhydrase 1, Gero antibody against the Gerbich blood group, or CD36 are usually positive. The differential diagnosis for erythroleukemia includes RAEB and AML with maturation with increased erythroid precursors and AML with multilineage dysplasia (involving ≥50% of myeloid or megakaryocyte-lineage cells). If erythroid precursors are 50% or more and the nonerythroid component is 20% or more, the diagnosis is erythroleukemia, whereas, if the nonerythroid component is less than 20%, the diagnosis is RAEB. The differential diagnosis for pure erythroid leukemia includes megaloblastic anemia secondary to vitamin B12 or folate deficiency, acute megakaryocytic leukemia, and ALL or lymphoma.[57]

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