Prognostic importance of morphology (FAB classification) in childhood acute lymphoblastic leukaemia (ALL)

The French-American-British (FAB) classification has been proposed as a useful and uniform method of defining morphologic subsets of acute leukaemias. As part of a prospective study designed to identify subsets of children with high risk of early relapse (CCG 141), submitted bone marrow slides from 765 of 883 patients entered on study were reviewed by two morphologists blinded as to prognostic factors and treatment regimen. L1, L2 and L3 acute lymphoblastic leukaemia (ALL) comprised 85.1%, 14.1% and 0.8%, respectively, of the total population. Children with greater than 25% L2 lymphoblasts had a significantly higher relapse rate and significantly poorer survival. Results of this study indicate that as a single variable, lymphoblast morphology is a very significant predictor of survival, haematologic remission, and complete continuous remission. Multivariate analyses show that lymphoblast morphology is again significant in determining duration of survival (P = 0.048), and is of borderline statistical significance (P = 0.089) in predicting length of complete continuous remission. The FAB classification, with minor modifications, is reproducible, useful, and prognostic in childhood ALL.