The WHO classification of AML encompasses 4 major categories:

(1) AML with recurring genetic abnormalities,

(2) AML with multilineage dysplasia,

(3) AML, therapy related, and

(4) AML not otherwise categorized.

 

In the first category the following subcategories are defined:

(a) AML with t(8;21)(q22;q22); AML1/ETO,

(b) AML with abnormal bone marrow eosinophils inv(16)(p13q22) or t(16;16)(p13;q22); CBFB/MYH11,

(c) acute promyelocytic leukemia (AML with t(15;17)(q22;q12); PML-RARA and variants)

(d) AML with 11q23/MLL abnormalities.

 

While a, b, and c are homogenous entities on the cytogenetic as well as at the molecular level and show close correlations with morphology, AML with 11q23/MLL abnormalities is heterogeneous due to the different partner chromosomes/partner genes.

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Acute myeloid leukemia (AML) with the t(8;21)(q22;q22) creating theAML1-ETO fusion gene is a distinct type of AML generally associated with a favorable. prognosis. The t(8;21)(q22;q22) is detected by conventional cytogenetic analysis in approximately 7% to 8% of cases of acute myeloid leukemia (AML).1The translocation generates a fusion gene located on the derivative chromosome 8, composed of the ETO gene on chromosome 8 and the AML1 gene (also knownas

RUNX1) on chromosome 21. The AML1-ETO fusion gene and its transcripts also can be detected by fluorescence in situ hybridization (FISH) and reverse transcriptase–polymerase chain reaction (RT-PCR).

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Acute myeloid leukemias (AMLs) carrying inv(16)/t(16;16) chromosomal abnormalities are associated with a good prognosis. acute myeloid leukemias (AML) is characterized by the presence of the fusion gene CBFb-Myh11. At the cytogenetic level, most of these patients are identified by the presence of an inversion of chromosome 16 [inv(16)(p13q22)] and rarely by a translocation t(16;16)(p13;q22).

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AML with 11q23/MLL rearrangement had a worse outcome, which was rather comparable with AML with unfavorable karyotype. Cytogenetic abnormalities in leukemia cells are strongly associated with distinct clinical subgroups and are predictive of both clinical features and therapeutic outcome. Recurrent cytogenetic abnormalities in chromosome 11q23 involving the mixed-lineage leukemia (MLL) gene have been observed in 3%–4% of adult patients with acute myeloid leukemia (AML), in 3%–7% of adults with acute lymphoblastic leukemia,5 and at even higher rate in infant leukemia.