Acute leukemias are a heterogeneous group of malignant diseases of hematopoietic progenitor cells with different molecular genetic abnormalities, clinical characteristics, and variable outcomes with currently available treatments. Age-specific incidence of acute myeloid leukemia (AML) rises linearly after age 40 with a median age of approximately 65 years. Most cases are sporadic, but congenital disorders such as Fanconi’s, Bloom’s, Down’s, Kostmann’s, and Diamond-Blackfan syndromes can increase the relative risk of developing AML (Scheinberg et al., 2001). Risk is also increased in individuals with acquired hematologic disorders including the myeloproliferative and myelodysplastic syndromes and paroxysmal nocturnal hemoglobinuria. Therapy-related AML (t-AML) may develop as a consequence of exposure to chemotherapy, including alkylating agents, epipodophyllotoxins, and ionizing radiation (Scheinberg et al., 2001). The age-specific incidence of acute lymphoblastic leukemia (ALL) peaks between the ages of 2 and 4, declines during late childhood adolescence and young adulthood, and peaks again among older adults. Mortality from ALL has declined dramatically during the last 25 years due to improvements in chemotherapy, particularly among children.