Natural Killer Cell Acute Leukemia

This form of leukemia typically falls under M0 [in the French—American—British (FAB) classification] or AML minimally differentiated (WHO classification). It is characterized by a unique immunophenotype, with both myeloid and natural killer cell markers, suggesting that it arises from a precursor common to both natural killer cell and myeloid lineages.56 The typical immunophenotype is CD33+, CD56+, CD11a+, CD13'°, CD15'°, CD34±, HLA-DR , CD16.56 Morphologically, the cells have deep invaginations in the nuclear membrane, scant cytoplasm, and fine azurophilic gran-ules.56 These granules often stain positive for myeloperoxidase and Sudan black B.56 Because of the morphology and absence of HLA-DR on flow cytometry, this entity can sometimes be confused with the microgranular variant of acute promyelocytic leukemia (APL).56 However, it lacks the characteristic translocation [t(15;17)] and patients tend to have a poor prognosis.56

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