Current concerns in haematology. 2: Classification of acute leukaemia.

Introduction For the past century the classification of leukaemia has been predominantly clinical and morphological, supplemented in recent decades by the application of cytochemical techniques. During the past five to 10 years major advances in our knowledge of the nature of leukaemia consequent on the application of the techniques of immunology, cytogenetics, and molecular genetics, have taken place. Such new techniques have not only advanced knowledge but are now being applied in the diagnosis of individual patients. Information gained has led haematologists to review clinical and haematological features and to reinterpret them in the light of immunological and cytogenetic characteristics of the clone of leukaemic cells. Within the major categories of acute myeloid leukaemia (AML) and acute lymphoblastic leukaemia (ALL) many new entities have been recognised which differ in their biological features, including their prognoses. The recognition of such entities is important in using new forms of treatment which may benefit patients with leukaemias which can not be cured with current protocols. The basis of the classification of acute leukaemia remains morphology and cytochemistry. Cases of acute leukaemia are most often classified according to predominant cell type as proposed by the FAB cooperative group.' 2 Information on immunophenotype and cytogenetic characteristics can be integrated with information derived from morphology and cytochemistry as is proposed in the MIC (Morphologic, Immunologic, and Cytogenetic) classifications of AML, ALL, and the myelodysplastic syndromes (MDS).?5 An alternative approach to the morphological classification of acute leukaemia that emphasises the number of lineages involved and the degree of maturation of leukaemic cells has been proposed.6