Leukemia is malignant neoplasms of the cells derived from either the myeloid or lymphoid line of the hematopoietic stem cells in the bone marrow. Proliferating abnormal and immature cells (blast) spill out into the blood and infiltrate the spleen, lymph nodes, and other tissue. Acute leukemias are characterized by rapid progression of symptoms. High numbers (greater than 50,000/mm3) of circulating blast weaken blood vessel walls, with high risk for rupture and bleeding, including intracranial hemorrhage. Lymphocytic leukemias involve immature lymphocytes and their progenitors. They arise in the bone marrows but infiltrate the spleen, lymph nodes, central nervous system (CNS), and other tissues. Myelogenous leukemias involve the pluripotent myeloid stem cells and, thus, interfere with the maturation of granulocytes, erythrocytes, and thrombocytes. Acute myelogenous leukemias (AML) and acute lymphatic leukemia (ALL) have similar
presentations and courses. Approximately half of new leukemias are acute. Approximately 85 % of acute leukemias in adults are AML, and incidence of AML increases with age. ALL is the most common cancer in children, with peak incidence between ages 2 and 9.
Although the cause of leukemias is unknown, predisposing factors include genetic susceptibility, exposure to ionizing radiation or certain chemicals and toxins, some genetic disorder (Down syndromes, Fanconi’s anemia), and human T-cell leukemia-lymphoma virus. Complications include infection, leukostasis leading to hemorrhage, renal failure, tumor lysis syndrome, and disseminating intravascular coagulation.
