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9 - Grade/differentiation unknown, not stated, or not applicable
Criteria for systemic mastocytosis met, and bone marrow aspirate shows 20% or more of cells are mast cells or 10% or more mast cells seen in circulating blood, shape of mast cells and nuclei have malignant features. No associated clonal hematologic non-mast cell disease. Aleukemic mast cell leukemia is a rare variant where <10% of circulating nucleated cells are mast cells.
Acute mast cell leukemia is an aggressive disorder with leukemic mast cells in blood and in large numbers in marrow. Mast cells must equal or exceed 20% of all nucleated cells in bone marrow aspirate smears. Bone marrow will show a diffuse, compact infiltrate of mast cells with a marked reduction of normal precursor blood cells and fat cells.