Acute myelomonocytic leukemia is an acute leukemia characterized by both myeloid and monocyte precursors.
Diagnostic Criteria (WHO 2016)
- ≥ 20% blasts (including promonocytes) in the bone marrow or peripheral blood
- Granulocytes and the precursors and monocyte and the precursors each constitute ≥ 20% of bone marrow cells
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Blood Film Features:
- Monoblast: large cells with large nucleus and abundant basophilic cytoplasm with some fine azurophilic granules and vacoules
- Promonocytes: large cells with large nucleus which are more irregular and slight convolution, basophilic cytoplasm with larger azurophilic granules and vacuoles
- Myeloblast
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Bone Marrow Features:
- Blast: Monoblast, promonocytes and myeloblast
- Granulocytes and the precursors and monocyte and the precursors each constitute ≥ 20% of bone marrow cells
- Cytochemistry: Myeloperoxidase – Positive, α-Naphthyl acetate esterase: Positive in monocytic cells ; inhibited by Sodium Floride
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Other features to look for:
- Eosinophilic precursors, some dysplastic with basophilic granules – suggestive of AML with eosinophilia (M4Eo), associated with the inv(16) cytogenetic abnormality.
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