AML M4 – Acute Myelomonocytic Leukaemia

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

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

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

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.

Other Resources

• ASH image bank: Acute myelomonocytic leukemia
• linical Flow Wiki: AML-M4