SECTION II: HEMATOLOGIC MALIGNANCIES
In contrast to the solid tumors, hematopoietic neoplasms are generally present diffusely at the outset, therefore demanding systemic therapy. Certain tumors of the hematopoietic system, particularly certain subtypes of the acute and chronic leukemias, despite their widespread nature, respond very well to therapy and are even curable with such a systemic approach. However, there is wide heterogeneity in the pathophysiology and natural history of the four main subtypes of acute and chronic leukemia: acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML), and chronic lymphocytic leukemia (CLL). The age distribution of these disorders varies widely, with ALL being a disease largely of children, CML of middle-aged adults, and AML and CLL having a median age in the seventh decade of life (1).