Acute monocytic leukemia

Acute monocytic leukemia
ICD-10	C93.0
ICD-9	206.0
MeSH	D007948

Template:Search infobox Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Synonyms and keywords: AMoL; AML-M5

Overview

Acute monocytic leukemia is considered a type of acute myeloid leukemia.

Classification

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).

Pathophysiology

Genetics

M5 is associated with characteristic chromosomal abnormalities, often involving 11q23 or t(9;11)affecting the MLL locus, however the MLL translocation is also found in other AML subtypes. MLL is believed to be prognostically unfavorable in AML-M5 compared to other genetic alterations involving MLL such as t(9;11) The t(8;16) translocation in MLL is associated with hemophagocytosis.

Immunology

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

Risk Factors

AML-M5 is thought to be associated with exposure to epidophyllotoxins.

Diagnosis

Diagnostic Criteria

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.

Laboratory Findings

• Peripheral Smear
  • 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.

Treatment

AML-M5 is treated with intensive chemotherapy (such as anthracyclines) or with bone marrow transplantation.

References

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