WHO-FAB Types and Classification of Acute Myeloid Leukemia (Acute Myelogenous Leukemia)

WHO and FAB have classified the types and classification of Acute Myeloid Leukemia (Acute Myelogenous Leukemia). Acute Myeloid Leukemia is much heterogeneous which reflects the complexities of myeloid cell differentiation. Who have proposed a classification and divided Acute Myeloid Leukemia into four categories.

Classification of Acute Myeloid Leukemia

The first classification of Acute Myeloid Leukemia includes the types that are associated with the specific genetic abnormality. This type is important because it is correlated with the guide therapy and prognosis. Other three categories of Acute Myeloid Leukemia come up after myelodysplastic disorder (MDS) or with therapy related Acute Myeloid Leukemia.

In classification of Acute Myeloid Leukemia the next two categories of Acute Myeloid Leukemia have different genetic features and therapy treatment response is too poor. The last category of Acute Myeloid Leukemia includes none of these features of all previous categories,

The classification of Acute Myeloid Leukemia was previously done according to the French-American-British (FAB) classification for the division of Acute Myeloid Leukemia. Although FAB classification of Acute Myeloid Leukemia is old but still it is referred in common practice.

Morphology: The diagnosis of Acute Myeloid Leukemia is based on at least 20% myeloid blast presence in the bone marrow. There are many types of myeloid blasts are identified and individual tumors may have more than one type of blasts with all features.

Classification of Acute Myeloid Leukemia

No.	Class	FAB Subtypes		Prognosis	Morphology
1	AML WITH GENETIC ABNORMALITY
	AML with t(8;21)(q22;q22); CBa/ETO fusion gene	M2	Favorable		Full range of Myelocytic maturation; Auer rods easily found; abnormal cytoplasmic granules
	AML with inv(16)(p13;q22); CBB/MYH11 fusion gene	M4eo	Favorable		Myelocytic and monocytic differentiation; abnormal eosinophilic precursors with abnormal basophilic granules
	AML with t(15;17)(q22;11-12); RARa/PML fusion gene	M3, M3v	Intermediate		Numerous Auer rods, often in bundles within individual progranulocytes; primary granules usually very prominent (M3 subtype), but inconspicuous in microgranular variant (M3v); high incidence of DIC
	AML with t(11q23;v); diverse MLL fusion genes	M4, M5	Poor		Usually some degree of monocytic differentiation
	AML with normal cytogenetics and mutated NPM	Variable	Favorable		Detected by immunohistochemical staining for NPM
2	AML ITH MDS-LIKE FEATURES
	With prior MDS	Variable	Poor		Diagnosis based on clinical history
	AML with multilineage dysplasia	Variable	Poor		Maturing cells with dysplastic features typical of MDS
	AML with MDS-like cytogenetic aberrations	Variable	Poor		Associated with 5q-, 7q-, 20q-aberrations
3	AML, THERAPY- RELATED	Variable	Very poor		If following alkylator therapy or radiation therapy, 2 – to 8 years latency period, MDS like cytogenetics aberrations and if following topoisomerase II inhibitor therapy 1 – 3 years latency period, translocations involving MLL (11q23)
4	AML, NOT SPECIFIED
	AML, minimally differentiated	M0	Intermediate		Negative for myeloperoxidase; myeloid antigens detected on blasts by flow cytometry
	AML without maturation	M1	Intermediate		> 3% of blasts positive for myeloperoxidase
	AML with myelocytic maturation	M2	Intermediate		Full range of myelocytic maturation
	AML with myelomonocytic maturation	M4	Intermediate		Myelocytic and monocytic differentiation
	AML with monocytic maturation	M5a, M5b	Intermediate		In M5 subtypes, non-specified esterase-positive monoblasts and pro-monocytes predominate in marrow and blood; in M5b subtype, mature monocytes predominate in blood
	AML with erythroid maturation	M6a, M6b	Intermediate		Erythroid/myeloid subtype (M6a) defined by 50% dysplastic maturing erythroid precursor and 20% myeloblasts; pure erythroid subtype (M6b) defined by > 80% erythroid precursors without myeloblasts
	AML with megakaryocytic maturation	M7	Intermediate		Blasts of megakaryocytic lineage predominate; detected with antibodies against megakaryocyte-specific markers (GPIIb/IIIa or vWF); often associated with marrow fibrosis; most common AML in Down syndrome
Ref: Pathologic Basis of Disease

Legends:

AML: Acute Myeloid Leukemia

DIC: Disseminated intravascular Coagulation

MDS: Myelodysplasia

NPM: Nucleophosmin

vWf: Von Willebrand Factor

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