About 3,800 new cases of acute lymphocytic leukemia (ALL) are diagnosed each year in the United States. It is the most common type of leukemia under the age of 15. Children are most likely to develop the disease, but it can occur at any age. Acute lymphocytic leukemia may be called by several names, including acute lymphoid leukemia and acute lymphoblastic leukemia.
ALL results from an acquired (not inherited) genetic injury to the DNA of a single cell in the bone marrow. The disease is often referred to as acute lymphoblastic leukemia because the leukemic cell that replaces the normal marrow is the (leukemic) lymphoblast. The effects are: 1) the uncontrolled and exaggerated growth and accumulation of cells called "lymphoblasts" or "leukemic blasts," which fail to function as normal blood cells and 2) the blockade of the production of normal marrow cells, leading to a deficiency of red cells (anemia), platelets (thrombocytopenia), and normal white cells (especially neutrophils, i.e., neutropenia) in the blood.
In most cases, the cause of acute lymphocytic leukemia is not evident. Few factors have been associated with an increased risk of developing the disease. Exposure to high doses of irradiation, as carefully studied in the Japanese survivors of atomic bomb detonations, is one such factor. Unlike other forms of leukemia, acute lymphocytic leukemia occurs at different rates in different locations. There are higher leukemia rates in more developed countries and in higher socioeconomic groups.
The current causes of acute lymphoblastic leukemia in children or adults are not known. Scientists continue to explore possible relationships with life-style or environmental factors but no firm conclusions have yet been reached. Given the amount of study, this suggests that multifaceted complex factors may be involved. It is extremely disconcerting to patients and their families to wonder what they may have done differently to avoid the disease. Unfortunately, at the present time there is no known way to prevent the disease. Acute lymphocytic leukemia occurs most often in the first decade of life but increases in frequency again in older individuals.
Acute lymphocytic leukemia can develop from primitive lymphocytes that are in various stages of development. The principal subtypes are uncovered by special tests on the leukemic lymphoblasts called "immunophenotyping." Phenotype is the physical characteristics of the cells and these are measured using immune tools. The subclassification of cell types is important since it helps to determine the best treatment to apply in each type of leukemia. The principle subtypes are T lymphocyte and B lymphocyte types, so named because the cell has features that are similar to normal T or B lymphocytes. In addition, the B cell type can be divided into a precursor B cell type, as well. Once these features are determined the term used may be acute T lymphoblastic leukemia or acute precursor (or pre) B cell lymphoblastic leukemia. Other markers on the lymphoblasts that can be detected with immunophenotyping and may be useful to the physician include the common acute lymphoblastic leukemia antigen, cALLa, now called CD 10.
Most patients feel a loss of well-being. They tire more easily and may feel short of breath when physically active. They may have a pale complexion from anemia. Signs of bleeding because of a very low platelet count may be noticed. These include black-and-blue marks occurring for no reason or because of a minor injury, the appearance of pinhead-sized, red spots under the skin, called petechiae, or prolonged bleeding from minor cuts. Discomfort in the bones and joints may occur. Fever in the absence of an obvious cause is common. Leukemic lymphoblasts may accumulate in the lymphatic system, and the lymph nodes can become enlarged. The leukemia cells can also collect on the lining of the brain and spinal cord and lead to headache or vomiting.
To diagnose the disease, the blood and marrow cells must be examined. In addition to low red cell and platelet counts, examination of the stained (dyed) blood cells with a light microscope will usually show the presence of leukemic blast cells. This is confirmed by examination of the marrow which almost always shows leukemia cells. The blood and/or marrow cells are also used for studies of the number and shape of chromosomes (cytogenetic examination), immunophenotyping, and other special studies, if required.
Courtesy of the Leukemia and Lymphoma Society.