After initial French‐American‐British (FAB) diagnosis by a multiinstitutional Southwest Oncology Group panel, slides of acute leukemia cases were recirculated to panel members for second review. The reproducibility of the FAB classification is analyzed. The classification is reproducible in the 70% range in panel reviewer hands and allows remarkable reproducibility in the morphologic and cytochemical distinction of acute lymphoid leukemia (ALL) from acute myeloid leukemia (AML). The limitations of a morphologic and cytochemical classification of acute leukemia are discussed. A simplification of the FAB system, merging M1, M2, and M4 as M7, is proposed; this simplification improves the system's reproducibility.
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