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		Overview of Leukemia

Acute myelomonocytic leukemia, acute monoblastic leukemia, and acute monocytic leukemia represent the myeloid leukemias with cytologic and cytochemical features of monocytic differentiation in the WHO classification. They correspond to acute myeloid leukemia (AML) FAB-M4, FAB-M5a, and FAB-M5b, respectively, in the French-American-British (FAB) classification. These 3 subtypes of AML differ solely in what percentage of immature cells show cytochemical evidence of monocytic differentiation and whether those immature cells are more or less mature. Promonocytes appear immature but retain some features of mature monocytes, such as folded and convoluted nuclear contours with a moderate amount of vacuolated cytoplasm. Monoblasts have an ameboid quality, with round to oval nuclei containing delicate chromatin, prominent nucleoli, and abundant cytoplasm.

By permission of the publisher. From Chang K, Forman S. In Atlas of Clinical Hematology. Edited by JO Armitage. Philadelphia, Current Medicine, 2004. Available at www.images.md.