Acute Myelomonocytic Leukemia

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Primary Author(s)*

Fei Yang, MD, FACMG
Oregon Health & Science University, Portland, OR

Cancer Category/Type

Acute Myeloid Leukemia

Cancer Sub-Classification / Subtype

Acute myelomonocytic leukemia

Definition / Description of Disease

Acute myelomonocytic leukemia is an acute leukemia characterized by the proliferation of both neutrophil and monocyte precursors. The peripheral blood or bone marrow has more than 20% blasts (including promonocytes). A minimum of 20% monocytes and their precursors is required for the morphological diagnosis, differentiating this entity from cases of AML with or without maturation that can present with a low-level of monocytes. In the 2016 revision to the World Health Organization (WHO) classification system, acute myelomonocytic leukemia is a distinct entity within the section of Acute Myeloid Leukemia (AML), Not Otherwise Specified[1][2]. This entity does not meet the criteria for inclusion in any of the other AML groups (i.e. AML with Recurrent Genetic Abnormalities, AML with Myelodysplasia-Related Changes, or Therapy-Related Myeloid Neoplasms).

Synonyms / Terminology

French-American-Brirish (FAB) classification M4, NOS

Epidemiology / Prevalence

Approximately 5-10% of AML cases, 3% of childhood leukemia

  • occurs in all age groups, but is more common in older individuals.
  • median patient age is 50 years
  • male-to-female ratio is 1.4:1

Clinical Features

The common clinical presentations are related to anaemia and thrombocytopenia, including fever, pallor, dyspnea, fatigue, loss of weight and bleeding disorders.

Sites of Involvement

Bone marrow

Morphologic Features

  • Monoblasts are large cells with abundant cytoplasm, which can be moderately to intensely basophillic, and round nuclei with delicate lacy chromatin and one or more predominant nucleoli; scattered azurophillic granuoles, vacuoles, and Auer rods may be present.
  • Promonocytes have a more irregular and delicately convoluted nuclear configuration and cytoplasm which is usually less basophillic and more granulated.
  • The peripheral blood typically shows an increase in monocytes, which are often more mature than those in the bone marrow.



  • ≥3% of blasts show myeloperoxidase (MPO) activity.
  • Monoblasts, promonocytes and monocytes usually show non-specific esterase activity.

Often a complex immunophenotype with multiple blast populations seen including:

  • immature blasts with high CD34 and/or KIT (CD117) expression
  • populations with myeloid markers: CD13, CD33, CD15, CD65 and MPO
  • populations with monocytic markers: CD4, CD11b, CD11c, CD14, CD64, CD36, CD68 (PGM1), CD163 and lysozyme
  • most cases are positive for HLA-DR
  • approximately 30% of cases are positive for CD7
Finding Marker
Positive (universal) EXAMPLE CD1
Positive (subset) EXAMPLE CD2
Negative (universal) EXAMPLE CD3
Negative (subset) EXAMPLE CD4

Chromosomal Rearrangements (Gene Fusions)

Characteristic Chromosomal Aberrations / Patterns

Myeloid-associated nonspecific cytogenetic abnormalities, such as trisomy 8, are present in most cases.

Genomic Gain/Loss/LOH


Gene Mutations (SNV/INDEL)

Acute myelomonocytic leukemia has genetic heterogeneity at the molecular level. Currently there is no specific gene identified that is frequently associated with this subset of AML.

Gene Mutation Oncogene/Tumor Suppressor/Other Presumed Mechanism (LOF/GOF/Other; Driver/Passenger) Prevalence (COSMIC/TCGA/Other)

Other Mutations

Type Gene/Region/Other
Concomitant Mutations EXAMPLE IDH1 R123H
Secondary Mutations EXAMPLE Trisomy 7
Mutually Exclusive EXAMPLE EGFR Amplification

Epigenomics (Methylation)


Genes and Main Pathways Involved


Diagnostic Testing Methods

  • Conventional chromosome analysis
  • FISH myeloid panel

Clinical Significance (Diagnosis, Prognosis and Therapeutic Implications)

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Familial Forms

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Other Information

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  1. Swerdlow SH, Campo E, Harris NL, Jaffe ES, Pileri SA, Stein H, Thiele J, Arber DA, Hasserjian RP, Le Beau MM, Orazi A, and Siebert R, Editors. World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues, Revised 4th edition. IARC Press: Lyon, France, p159-160.
  2. Arber, Daniel A.; et al. (2016). "The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia". Blood. 127 (20): 2391–2405. doi:10.1182/blood-2016-03-643544. ISSN 1528-0020. PMID 27069254.


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