Acute Myeloid Leukemia
Gladstone E. Airewele
C. Philip Steuber
Acute myeloid leukemia (AML) represents approximately 20% of all leukemia diagnosed in children. In the United States, about 500 new cases are diagnosed annually in children less than 15 years old. Unlike acute lymphoid leukemia (ALL), the incidence of AML remains stable from birth until 10 years of age, and the disease occurs with equal frequency in boys and girls and in the various ethnic groups. The factors that lead to the development of AML are unknown in the overwhelming majority of cases, but certain conditions and exposures are known to predispose to AML (Box 301.1). In general, AML cells are more resistant to chemotherapy compared to ALL, and the therapy for childhood AML has not reached the degree of success achieved for ALL. Nevertheless, major therapeutic improvements have occurred in the last 20 years, and the overall long-term survival now approaches 50% to 60% in some studies. This improvement has been due largely to clinical trials conducted by various childhood cancer treatment groups and also to improvement in general supportive-care capabilities.
AML is the result of a clonal proliferation of a hematopoietic precursor cell. The abnormal proliferation results in an accumulation of immature myeloid cells that are incapable of differentiating into mature cells. Although the precise pathophysiology of AML development is not completely understood, as in other malignancies, this abnormal proliferation results from a series of mutations affecting genes that are responsible for regulating the proliferation and differentiation of the hematopoietic stem cell. The term AML includes a variety of leukemia subtypes that are designated by apparent cell of origin (Table 301.1).
TABLE 301.1. THE FAB CLASSIFICATION SYSTEM WITH TYPICAL IMMUNOPHENOTYPING
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