M3 Granular or hyper-granular promyelocytes. The neutrophils are often normal, occasionally dysplastic. Erythroid precursors and megakaryocytes do not show significant abnormalities. Immunofluorescence for PML nuclear protein. Promyelocytes are agranular with deeply basophilic cytoplasm.
Bilobed nuclei are a prominent feature.
Cytochemistry, cytogenetics and molecular studies as for classical M3. The PML nuclear protein pattern is confirmatory and quick to do. Mixture of smaller myeloblasts and larger monoblasts. CAE and ANAE stains to confirm cells of both granulocyte and monocyte lineages are present. The proportion of granulocytic and monocytic cells are highly variable.