The classification of acute leukaemia (AL) and its clinical significance.

The combination of morphological, cytochemical and immunological methods has resulted in a reproducible and more objective classification of AL. Several of the AML-FAB subtypes (M2, M3 and M5) correlate with specific chromosome abnormalities and are associated with distinct clinical and laboratory features. The classification of ALL based on morphology (FAB types L1, L2 and L3) has been shown to have prognostic value. The heterogeneity of ALL is better recognised by membrane marker analysis, now improved by the use of monoclonal antibodies. The enzyme terminal transferase is the best marker for lymphoblasts and helps in the differential diagnosis between ALL and AML. Cases of undifferentiated AL and rare types of AML can be identified by ultrastructural cytochemistry. The clinical significance of the classification of AL is briefly discussed.