Acute
leukemias are a heterogeneous group of
malignancies with varying clinical, morphologic, immunologic, and molecular characteristics. Many distinct types are known to carry predictable prognoses and warrant specific
therapy. Distinction between lymphoid and
myeloid leukemias, most often made by flow cytometry, is crucially important. Several advances in flow cytometry, including availability of new
monoclonal antibodies, improved gating strategies, and multiparameter analytic techniques, have all dramatically improved the utility of flow cytometry in the diagnosis and classification of
leukemia. Acute
leukemias reflect the pattern of
antigen acquisition seen in normal hematopoietic differentiation, yet invariably demonstrate distinct aberrant immunophenotypic features. Detailed understanding of these phenotypic patterns of differentiation, particularly in
myeloid leukemia, allows for more precise classification of
leukemia than does morphology alone. However, morphologic and differentiation-based classifications of
leukemia are limited in their prognostic value; cytogenetics and molecular genetics appear to be most important for identifying entities with distinct prognoses and clinical behavior. Increasingly, many of these genetically distinct subgroups of
leukemia have been found to be closely associated with distinct immunophenotypes. For example, translocations such as t(8;21), t(15;17), and inv(16) in
acute myeloid leukemia (AML), and t(1;19) and t(12;21) in
acute lymphoblastic leukemia (ALL) have distinctive immunophenotypic profiles. Thus, in addition to classification into differentiation-based subtypes, detailed flow cytometric studies can define complex antigenic profiles that are associated with specific molecular defects and well-defined biology. In summary, multiparameter flow cytometry is an invaluable tool in the diagnosis, classification, and monitoring of patients with acute
leukemia. Semin Hematol 38:124-138.