Acute myeloid leukemia classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Raviteja Guddeti, M.B.B.S. [2]

Overview

Acute myeloid leukemia may be classified according to the French-American-British (FAB) classification and World Health Organization (WHO). The French-American-British (FAB) classification system is divided into 8 subtypes: Subtype M0 Minimally differentiated AML, Subtype M1 Acute myeloblastic leukemia, without maturation Subtype M2 Acute myeloblastic leukemia with granulocytic maturation, t(8;21)(q22;q22), t(6;9), Subtype M3 Promyelocytic, or Acute promyelocytic leukemia (APL), t(15;17), Subtype M4 Acute myelomonocytic leukemia, inv(16)(p13q22), del(16q), Subtype M4eo, Myelomonocytic together with bone marrow eosinophilia, inv(16), t(16;16), Subtype M5 Acute monoblastic leukemia (M5a) or Acute monocytic leukemia (M5b) del (11q), t(9;11), t(11;19)SubtypeM6 Acute erythroid leukemias, including erythroleukemia (M6a) and very rare pure erythroid leukemia (M6b), Subtype M7 Acute megakaryoblastic leukemia, t(1;22). World Health Organization (WHO) classification of acute myeloid leukemia is divided in four categories and subcategories; AML with characteristic genetic abnormalities, AML with multilineage dysplasia, AML and MDS, therapy-related and AML not otherwise categorized.

Classification

There are 2 classifications systems for acute myeloid leukemia, the French-American-British (FAB) classification and the World Health Organization (WHO):

French-American-British classification

The 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 its degree of maturity. This is done by examining the appearance of the malignant cells under light microscopy and/or by using cytogenetics to characterize any underlying chromosomal abnormalities. The subtypes have varying prognoses and responses to therapy. Although the WHO classification (see below) may be more useful, the FAB system is still widely used as of mid-2006.

The eight FAB subtypes are:

Type	Name	Cytogenetics
M0	Minimally differentiated AML
M1	Acute myeloblastic leukemia, without maturation
M2	Acute myeloblastic leukemia, with granulocytic maturation	t(8;21)(q22;q22), t(6;9)
M3	Promyelocytic, or Acute promyelocytic leukemia (APL)	t(15;17)
M4	Acute myelomonocytic leukemia	inv(16)(p13q22), del(16q)
M4eo	Myelomonocytic together with bone marrow eosinophilia	inv(16), t(16;16)
M5	Acute monoblastic leukemia (M5a) or Acute monocytic leukemia (M5b)	del (11q), t(9;11), t(11;19)
M6	Acute erythroid leukemias, including erythroleukemia (M6a) and very rare pure erythroid leukemia (M6b)
M7	Acute megakaryoblastic leukemia	t(1;22)

World Health Organization classification

The World Health Organization (WHO) classification of acute myeloid leukemia attempts to be more clinically useful and to produce more meaningful prognostic information than the FAB criteria. Each of the WHO categories contains numerous descriptive sub-categories of interest to the hematopathologist and oncologist; however, most of the clinically significant information in the WHO schema is communicated via categorization into one of the five subtypes listed below.

The WHO subtypes of AML are:

Name	Description	ICD-O
AML with characteristic genetic abnormalities	Includes: AML with translocations between chromosome 8 and 21 [t(8;21)] (ICD-O 9896/3); RUNX1/RUNX1T1 AML with inversions in chromosome 16 [inv(16)] (ICD-O 9871/3); CBFB/MYH11 APL with translocations between chromosome 15 and 17 [t(15;17)] (ICD-O 9866/3); RARA;PML Patients with AML in this category generally have a high rate of remission and a better prognosis compared to other types of AML.	Multiple
AML with multilineage dysplasia	This category includes patients who have had a prior myelodysplastic syndrome (MDS) or myeloproliferative disease (MPD) that transforms into AML. This category of AML occurs most often in elderly patients and often has a worse prognosis.	Template:ICDO
AML and MDS, therapy-related	This category includes patients who have had prior chemotherapy and/or radiation and subsequently develop AML or MDS. These leukemias may be characterized by specific chromosomal abnormalities, and often carry a worse prognosis.	Template:ICDO
AML not otherwise categorized	Includes subtypes of AML that do not fall into the above categories.	Template:ICDO

Acute leukemias of ambiguous lineage (also known as mixed phenotype or biphenotypic 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.

References

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