Overview of the Leukemias

Abstract

The previous chapter described malignant cells that originate in lymphoid organs, such as lymph nodes and the spleen. Leukemias are also cancers of the immune system, but these neoplasms originate within hematopoietic stem and progenitor cells in the blood and bone marrow. Leukemias can arise from lymphoid cells (B cells and T cells), like lymphomas, or from cells of the myeloid lineage. Clonal expansion of one cell line results in underproduction of normal red blood cells, platelets, and other leukocytes. Cytopenias lead to requirement for blood product transfusions. Also, cytopenias result in weakening of the immune system and increased risk of infection, which is the most common cause of death in patients with leukemia. Importantly, leukemias not only occupy the bone marrow space, but can also infiltrate organs such as the liver, spleen, skin, and central nervous system (CNS). Major CNS consequences result from leptomeningeal spread of disease, parenchymal infiltration by leukemia cells, paravertebral masses leading to spinal cord or cauda equina compression, hemorrhage in the setting of disseminated intravascular coagulation, and leukostasis. These CNS complications can cause central and peripheral nerve palsies, seizures, and altered sensorium. Treatment of CNS involvement may involve leukapheresis, radiation, intrathecal chemotherapy, and systemic chemotherapy using agents capable of traversing the blood-brain barrier.