- Criteria for diagnosis: myeloblasts, monoblasts and promonocytes are 20% or more of nonerythroid cells; myeloblasts and granulocytes are 80% or less of nonerythroid cells; monocyte lineage cells are 20% or more of nonerythroid bone marrow cells
- If less than 20% of bone marrow cells are monocyte lineage, still M4 if blood monocyte count is 5x109/L or higher
- Additional criteria (if cannot distinguish early monocytes and early granulocytes): nonspecific esterase reactivity in 20% or more cells or serum lysozyme of 3 times normal
- 5 - 10% of AML cases, 3% of childhood leukemia (Orphanet May 2004: Acute myelomonocytic leukemia [Accessed 4 April 2018])
- Children and adults; more common in adults; median age 50 years; male:female is 1.4:1
- Often markedly elevated WBC with anemia and thrombocytopenia, fever, fatigue, variable blasts and promonocytes in peripheral blood; organomegaly, lymphadenopathy and other tissue infiltration (monocytes infiltrate)
- May occur post-therapy (Sichuan Da Xue Xue Bao Yi Xue Ban 2007;38:347)
- Enzyme cytochemistry: monoblasts, promonocytes and monoctes are positive for nonspecific esterase; if negative, confirm monocyte lineage with immunophenotyping or EM; at least 3% of blasts are MPO+; double staining for NSE and CAE or MPO may show dual positive cells
- 15 year old girl with catastrophic antiphospholipid antibody syndrome (J Pediatr Hematol Oncol 2004;26:327)
- 21 year old man with AML mimicking primary testicular neoplasm (Eur J Haematol 2003;70:242)
- 23 year old pregnant woman with CD15, CD33 and HLA-DR+ antibodies (The Internet Journal of Hematology 2003;1:1)
- 27 year old man with leukemic ascites (Arch Pathol Lab Med 2005;129:262)
- Myelocytic and monocytic differentiation evident
- Myeloid cells resemble M2 (60% of myeloblasts have Auer rods), but at least 20% of nonerythroid cells are of monocytic lineage
- Monoblasts are large cells with abundant cytoplasm, moderately to intensely basophilic, may have pseudopod formation, scattered fine azuophilic granules and vacuoles
- Round nuclei with lacy chromatin and one or more large nucleoli
- Promonocytes have abundant, less basophilic cytoplasm which is more obviously granulated with occasional large azurophilic granules and vacuoles, is more irregular and has delicately folded nuclei
Myeloblast (upper left) with two long slender Auer rods, neutrophilic myelocyte (below myeloblast) with smudged nonspecific
granules and promonocyte (right) with abundant azurophilic granules and nucleus with delicate folds and creases
Bone marrow smears (Wright-Giemsa):
Mixture of monocytes and neutrophils at
different stages of maturation, also several
promonocytes with abundant cytoplasm
containing fine azurophilic granules and
delicately folded nuclei
Promonocytes on left have basophilic cytoplasm with
coarse azurophilic granules; those in upper right have
abundant pale cytoplasm with delicate nuclear folds
Three promonocytes have abundant
cytoplasm with fine azurophilic granules,
also dysplastic neutrophil with pseudo-
Pelger-Huet nucleus in upper left
Five promonocytes and two myelocytes (center),
one containing numerous azurophilic granules and an Auer rod
Bone marrow biopsy:
Markedly hypercellular marrow with heterogeneous cells, including
immature monocytes (irregular nuclei and prominent nucleoli) and neutrophils
Stains:
Chloroacetate esterase stains neutrophils blue,
and nonspecific esterase stains monocytes red-brown
Images hosted on other servers:
Bone marrow biopsy:
Resembling sarcomatoid carcinoma
Other sites:
Leukemic ascites
Stains:
Nonspecific esterase
CD68
Lysozymes
Peroxidase (myeloid marker)
- CD41, CD61, glycophorin A and keratin
- Nonspecific cytogenetic abnormalities, +8 in most cases
- Classify as AML with recurrent genetic abnormalities if inv(16)(p13;1q22), t(16;16)(p13.1q22) or t(9;11)(p22;q23) present
- AML M2
- AML with recurrent genetic abnormalities
- CMML
- G-CSF related transient atypical monocytosis (Clin Lab Haematol 2004;26:359)
- Leukemoid reaction
- M5
- Microgranular M3
- t-AML (therapy related)
- Myelodysplastic syndrome
- Sarcomatoid carcinoma
