The traditional classification of acute leukemia used criteria proposed by the French– American–British Cooperative Group (FAB) , using the 30% bone marrow blast cell cutoff (Bennett et al, 1985). This classification system originally distinguished different leukemia types by morphologic features and cytochemical studies, particularly myeloperoxidase (or Sudan black B) and non-specific esterase staining. It was revised to include leukemia types that could only be accurately identified with the addition of immunophenotyping or electron microscopic studies (Bennett et al., 1991)
