Acute monocytic leukemia


Acute monocytic leukemia is a type of acute myeloid leukemia.

Causes

M5 is associated with characteristic chromosomal abnormalities, often involving chromosome 11, such as t, affecting the MLL locus at 11q23; however MLL translocations are also found in other leukemia subtypes. The t 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 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 is made depending on whether the monocytic cells are predominantly monoblasts or a mixture of monoblasts and promonocytes. 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, however NSE may often be negative.
Immunophenotypically, M5-AML variably express myeloid and monocytic markers. Cells may aberrantly express B-cell marker CD20 and the NK marker CD56. Monoblasts may be positive for CD34.

Treatment

AML-M5 is treated with intensive chemotherapy or with bone marrow transplantation.