Acute monoblastic leukemia

Other Names: Acute myeloblastic leukemia type 5; Acute monocytic leukemia; AML-M5; AML M5

Acute monoblastic leukemia (AML-M5), is one of the most common subtypes of acute myeloid leukemia (AML; see this term) that is either comprised of more than 80% of monoblasts (AML-M5a) or 30-80% monoblasts with (pro)monocytic differentiation (AML-M5b). AML-M5 presents with asthenia, pallor, fever, and dizziness. Specific features of AML-M5 include hyperleukocytosis, propensity for extramedullary infiltrates, coagulation abnormalities including disseminated intravascular coagulation and neurological disorders. Leukemia cutis and gingival infiltration can also be seen. A characteristic translocation observed in AML-M5 is t(9;11).

Causes

M5 is associated with characteristic chromosomal abnormalities, often involving chromosome 11, such as t(9;11), affecting the MLL (KMTA2) locus at 11q23; however MLL translocations are also found in other leukemia subtypes. The t(8;16) translocation in AMoL is associated with hemophagocytosis.

Secondary leukaemia, which may include AML-M5, has been associated with exposure to epipodophyllotoxins, such as etoposide.

Diagnosis

In order to fulfill World Health Organization (WHO) criteria for AML-5, a patient must have greater than 20% blasts in the bone marrow, and of these, greater than 80% must be of the monocytic lineage.

A further subclassification (M5a versus M5b) is made depending on whether the monocytic cells are predominantly monoblasts (>80%) (acute monoblastic leukemia) or a mixture of monoblasts and promonocytes (<80% blasts).

Monoblasts can be distinguished by having a roughly circular nucleus, delicate lacy chromatin, and abundant, often basophilic cytoplasm. These cells may also have pseudopods.

By contrast, promonocytes have a more convoluted nucleus, and their cytoplasm may contain metachromatic granules. Monoblasts are typically MPO-negative and promonocytes are MPO variable. Both monoblasts and promonocytes stain positive for non-specific esterase (NSE), however NSE may often be negative.

Immunophenotypically, M5-AML variably express myeloid (CD13, CD33) and monocytic (CD11b, CD11c) markers. Cells may aberrantly express B-cell marker CD20 and the NK marker CD56. Monoblasts may be positive for CD34. Immunophenotyping

• CD4 expression
• CD11b expression
• CD11c expression
• CD13 expression
• CD14 expression
• CD15 expression
• CD33 bright expression
• CD34 positive
• CD36 bright expression
• CD64 bright expression
• CD65 expression
• CD68 expression
• HLA-DR positive
• Lysozyme expression
• KIT (CD117) expression
• MPO expression

Definitive Diagnostic Methods

• Bone marrow biopsy
• Flow cytometry
• Genetic testing
• Histologic confirmation
• Immunophenotyping

Treatment

AML-M5 is treated with intensive chemotherapy (such as anthracyclines) or with bone marrow transplantation. Hematologic Transplant and/or Endocrine Procedures are considered

NIH genetic and rare disease info

• NIH info on Acute monoblastic leukemia

Acute monoblastic leukemia is a rare disease.

Acute monoblastic leukemia Resources
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