Classification

Earlier AML was classified morphologically into specific subtypes by the French, American, British (FAB) group:

• M0, undifferentiated undifferentiated blasts myeloblastic identified by myeloid monoclonal antibodies or peroxidases;
• M1, myeloblastic w/o predominantly myeloblasts, maturation little or no maturation;
• M2, myeloblastic with myeloblasts and promyelocytes, maturation further maturation abnormal
• M3, promyelocytic predominantly promyelocytes, often hypergranular
• M4, myelomonocytic evidence of both granulocytic + monocytic maturation, > 20% in blood or marrow
• M5, monocytic predominantly monoblasts (M5a) or promonocytes (M5b)
• M6, erythroleukaemia > 50% erythroblasts, often bizarre, multinucleate, megaloblastic
• M7, megakaryocytic predominantly megakaryocytes or micromegakaryocytes, often associated with acute myelofibrosis

However this has been superseded by the more recent World Health Organization (WHO) classification (1). It differs from the FAB from the following:

• blast percentage in marrow which separates myelodysplastic syndrome (MDS) from AML is reduced from 30% to 20%
• taking account of preceding MDS or myeloproliferative disorders
• creating categories defined by certain non-random cytogenetic abnormalities or the equivalent molecular genetic abnormality (t(8;21), t(15;17), inv(16)/t(16;16) and t(v;11q23).
• taking account of multilineage dysplasia with or without a preceding marrow disorder
• recognising previous cytotoxic therapy as part of the classification
• introducing new morphological subtypes (1).

Reference:

• (1) British Committee for Standards in Haematology et al.Guidelines on the management of acute myeloid leukaemia in adults. Br J Haematol. 2006;135(4):450-74.