Chapter 450

Acute myeloid leukemia (AML) accounts for about 20% of cases of acute leukemia in children and 80% of cases of acute leukemia among adults. Further, although AML is significantly less common than acute lymphoblastic leukemia (ALL) in childhood, the survival for children with AML is current between 50% and 60% compared to nearly 85% of children with ALL. In addition, the treatment for children with AML remains particularly toxic and includes multiple, near myeloablative courses of treatment with chemotherapeutic agents and often hematopoietic stem cell transplantation (HSCT). As chemotherapeutic regimens have achieved higher cure rates in selected patients with good prognostic characteristics, HSCT is currently recommended primarily for patients with very high-risk disease characteristics or those who relapse and achieve a second remission. Insights into stem cell physiology and the molecular basis of AML have demonstrated some of the fundamental molecular changes driving the behavior of the leukemia, revealed their extensive heterogeneity, and have begun to provide new therapeutic targets and strategies.

The chronic myeloid forms of leukemia are extremely rare in children. These myeloproliferative syndromes most commonly include the adult type of Philadelphia-chromosome-positive (Ph+), chronic myelogenous leukemia (CML), and juvenile myelomonocytic leukemia (JMML). The clinical course, biologic characteristics, and molecular pathogenesis of CML and JMML are quite different. Until recently, allogeneic bone marrow transplant (BMT) from either a related or an unrelated donor was the management of choice for children with Ph + CML but the kinase inhibitor imatinib has changed the treatment paradigm for that disease in both children and adults, although hematopoietic stem cell transplantation (HSCT) is still the only know curative therapy for CML. An allogeneic HSCT remains the only know curative option for children with JMML.

### Epidemiology

The annual incidence of acute myeloid leukemia (AML) in children remains constant, with the exception of a slight peak in infants and during adolescence. After age 20 years, the incidence of AML slowly increases with age. Infants with congenital leukemia are more likely to have AML than acute lymphoblastic leukemia (ALL). Although the incidence of AML in children in the United States is approximately 7 cases per million children per year or approximately 600 new cases per year, there is a slightly higher incidence in Hispanic children of 9 per million per year. The incidence also appears slightly higher in Japan, Australia, and Zimbabwe. Of note, the incidence of AML has been increasing slightly although steadily.

The cause of AML is unknown, and most children have no known predisposing factors. Known risk factors include exposure to high-dose ionizing radiation, previous chemotherapy (especially with alkylating agents and epipodophyllotoxins), Down syndrome, congenital bone marrow failure syndromes (Diamond-Blackfan anemia and Kostmann agranulocytosis; see Chapter 430), chromosome fragility and impaired DNA repair mechanisms (such as Fanconi anemia), and inherited disorders, such as neurofibromatosis type I (NF1), which is due to mutations in neurofibromin, a RAS-directed GTPase (see Chapter 182). Children with NF1 are at ...

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