1.Laboratoire d Hématologie, Hôpital Necker-Enfants Malades, Paris, France
DEFINITION: The translocation t(8;21)(q22;q22) is one of the most common structural aberration in acute myeloid leukemia and is found in 5-12% of AML and in one-third of karyotypically abnormal M2 cases according to the French-American-British (FAB) classification. MORPHOLOGY AND CYTOCHEMISTRY: Among the non-random chromosomal aberrations observed in AML, t(8;21)(q22;q22) is one of the best known and usually correlates with AML M2, with well defined and specific morphological features. AML M2 FAB is the morphological type predominating in correlation with t(8;21), but some AML M1 or AML M4 cases have been also reported. Rare cases with a low bone marrow blast cell count (
The classification of acute myeloid leukemia (AML) and myelodysplasic syndromes (MDS) includes clinical data (previous history, age) and biologic characteristics (morphology, cytochemistry, immunophenotype, cytogenetic and molecular biology). The separation of homogeneous classes allows us to distinguish pronostic parameters and to identify groups of patients sensitive to drugs or to specific treatment. Recurrent cytogenetic abnormalities are strong prognostic indicators in AML and MDS. Molecular studies of structural chromosomal changes have enabled the cloning of genes located at chromosomal breakpoints and have helped to characterize the proteins involved in leukemogenesis. Morphologic studies remain important because of a strong correlation with cytogenetic and molecular abnormalities.
The clinico-biological classification of acute myeloid leukemia (AML) should include morphological, cytochemical, immunophenotypic, cytogenetic and molecular characterization of the leukemia blasts. The identification of homogeneous categories would allow the development and refinement of treatment strategies.- Recurrent cytogenetic abnormalities are important as prognostic indicators in AML. The identification of specific abnormalities is used increasingly to decide treatment. Cytogenetic findings have contributed to the understanding of morphological and clinical heterogeneity of AML. Molecular genetic analysis of recurrent translocations and inversions has led to clone genes adjacent to chromosome breakpoint and to characterize their protein products involved in the leukemogenesis process.- Over the years, leukemia classifications have been mainly descriptive, which was open to regular criticism, revision and reassessment. During the last 20 years, classification according to morphological features of leukemia has been proposed (F.A.B. defined classification). This classification is based on cell morphology on May-Grunwald-Giemsa (MGG) staining of peripheral blood and bone marrow smears with the addition of simple cytochemical techniques
Rationale for a new classification approach - The age-incidence of AML is subtly bimodal. Between early childhood and age 45, the annual incidence of acute myeloid leukemia (AML) remains constant at 0.8 cases/105population. The incidence rises exponentially after the age of 45, exceeding 15 cases/105 population by age 75. AML has been extensively characterized using cytogenetic since the mid-1970s.- Available data have suggested an alternative classification in four main groups; a first one for patients identified with specific balanced translocations, the second group for patients with "multilineage" deregulation, a third one for "secondary" AML (after exposure to mutagenic agent or chemo/radiotherapy). Although this is a more rational model of AML classification, some patients cannot be classified into the three first groups and defined a fourth group. At least for the moment, the diagnosis of this last group of patients must rely on the classical cytologic approach (FAB) defining "morphological"-based category.
Georges Flandrin
Classification of acute myeloid leukemias
Atlas Genet Cytogenet Oncol Haematol. 2002-05-01
Online version: http://atlasgeneticsoncology.org/haematological/1238/classification-of-acute-myeloid-leukemias