Median age at diagnosis is 50 years. Rarely presenting symptoms are due to chloromas or CNS involvement. Cytoplasm shows variable basophilia. A few granules or Auer rods may be present. Maturing granulocytes may be normal or show the dysplastic features seen in MDS .
Monoblasts are generally very large with abundant grey-blue or basophilic cytoplasm.
Nuclei are round or lobulated, and are central in the cell. Fine azurophil granules may be present but Auer rods are rarely, if ever, present. Promonocytes and monocytes show abnormal nuclear maturation, granulation and loss of basophilia. Erythroid precursors may be normal or show varying degrees of dyserythropoiesis. Eosinophils may be present in varying numbers, with normal or abnormal morphology.