Acute myelocytic leukemia

Acute myelogenous leukemia (AML), also known as acute myeloid leukemia, is a cancer of the myeloid line of blood cells. The median age of patients with AML is 70; it is rare among children. more...

Myeloid leukemias are characterized as "acute" or "chronic" based on how quickly they progress if not treated. Chronic myelogenous leukemia (CML) is often without symptoms and can remain dormant for years before transforming into a blast crisis, which is markedly similar to AML.

Pathophysiology

Specific chromosomal abnormalities are seen in patients with some forms of AML. These chromosomal abnormalities tend to disrupt genes that encode for transcription factors needed for myeloid stem cells to differentiate into specific blood components. Without differentiation occurring, these myeloid precursor cells fill the bone marrow and spill out into the blood. The overpopulation of the bone marrow with myeloid precursors also results in supression of normal marrow stem cells, giving rise to the symptoms of anemia (lack of red blood cells), thrombocytopenia (lack of platelets), and neutropenia (lack of neutrophils).

Subtypes

World Health Organization (WHO) classification

The World Health Organization (WHO) classification of acute myeloid leukemia (AML) attempts to be more applicable and produce more meaningful prognostic information then the older French-American-British (FAB) criteria, described below.

The WHO criteria are:

• AML with characteristic genetic abnormalities, which includes AML with translocations between chromosome 8 and 21 , inversions in chromosome 16 and acute promyelocytic leukemia (APL). Patients with AML in this category generally have a high rate of remission and a better prognosis compared to other types of AML.
• AML with multilineage dysplasia. This category includes patients who have had prior myelodysplastic syndrome (MDS) or a myeloproliferative diseases (MPD) that transforms into AML. This category of AML occurs primarily in elderly patients
• AML and MDS, therapy related. This category includes patients who have had prior chemotherapy and/or radiation and subsequently develop AML or MDS.
• AML not otherwise categorized. Includes subtypes of AML that do not fall into the above categories.
• Acute leukemias of ambiguous lineage. Acute leukemias of ambiguous lineage (also known as mixed phenotype acute leukemia) occur when the leukemic cells can not be classified as either myeloid or lymphoid cells or where both types of cells are present.

French-American-British (FAB) classification

The older French-American-British (FAB) classification system divided AML into 8 subtypes, M0 through to M7 based on the type of cell from which the leukemia developed and degree of maturity. This is done by examining the appearance of the malignant cells under light microscopy or cytogenetically by characterization of the underlying chromosomal abnormality. Each subtype is characterised by a particular pattern of chromosomal translocations and have varying prognoses and responses to therapy. Although the WHO classification is more useful, the FAB system is still in use.

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