Pathophysiology
Clinical meaning
Leukemia is a group of malignant neoplasms affecting the blood-forming tissues of the bone marrow, resulting in the uncontrolled proliferation of abnormal white blood cells (blasts) that crowd out normal hematopoietic cells. Under normal conditions, hematopoietic stem cells in the bone marrow differentiate along two primary lineages: the myeloid lineage (producing red blood cells, platelets, monocytes, granulocytes) and the lymphoid lineage (producing B lymphocytes, T lymphocytes, natural killer cells). In leukemia, a genetic mutation occurs in a precursor cell, causing it to replicate without proper differentiation. These immature blast cells accumulate in the bone marrow and eventually spill into the peripheral blood, infiltrate the spleen, liver, lymph nodes, and central nervous system. Leukemia is classified by the cell lineage affected and by the speed of disease progression. Acute leukemias (acute lymphoblastic leukemia [ALL] and acute myeloid leukemia [AML]) involve rapidly proliferating immature blast cells that do not mature into functional cells; these diseases progress rapidly and are life-threatening without treatment. ALL is the most common childhood malignancy, with peak incidence between 2 and 5 years of age, while AML is...