Leukemia, << loo KEE mee uh, >> is a cancer of the bone marrow, which is the soft, spongy, blood-forming tissue within bones. Bone marrow produces three types of blood cells: (1) white blood cells that fight infections; (2) red blood cells that carry oxygen from the lungs to the rest of the body; and (3) platelets, tiny blood cells that help stop bleeding. In leukemia, large numbers of abnormal white blood cells multiply in an uncontrolled manner in the bone marrow and crowd out normal blood cells. In addition, the abnormal white blood cells do not fight infections.
Symptoms of leukemia include fevers and infections. Fatigue, anemia (a lack of functioning red blood cells), and bleeding or bruising due to low platelet count are also among the symptoms of the disease. See Anemia .
Leukemia is classified as acute or chronic, depending on how quickly it develops. The disease is also classified by the type of white blood cells affected. The most common types of white blood cells are lymphoid and myeloid, and each kind fights certain infections. When leukemia affects lymphoid cells, it is called lymphocytic leukemia. Leukemia that affects myeloid cells is called myeloid or myelogenous leukemia. Both lymphocytic and myeloid leukemia may be acute or chronic.
Acute leukemias
develop extremely quickly. Abnormal, immature white blood cells multiply rapidly, and the number of normal cells decreases sharply. Acute lymphocytic leukemia is the most common leukemia in children. About 70 percent of children with this leukemia can be cured with current treatments.
The most common treatment for acute lymphocytic leukemia is chemotherapy, the use of chemicals to kill the cancer cells. Radiation therapy may be combined with chemotherapy to treat this leukemia. Radiation therapy uses high-energy X-rays to kill cancer cells. Another treatment is bone marrow transplant, in which the diseased bone marrow is destroyed and replaced with healthy bone marrow from a donor.
All treatments for acute leukemias are intensive and may endanger the patient’s life. The use of powerful antibiotics and of blood transfusions has increased the chances of surviving the intensive therapy.
Acute myeloid leukemia usually strikes adults. Chemotherapy is the preferred treatment for this leukemia. Seventy percent of patients receiving chemotherapy enter remission. During remission, the blood cells and bone marrow return to normal. Patients are considered cured if they remain in remission for at least two years. However, only 25 percent of patients with acute myeloid leukemia remain in remission and are cured.
Chronic leukemias
develop more slowly than acute leukemias. In chronic leukemias, the abnormal white blood cells appear mature and resemble normal white blood cells. In the early stages of the disease, the abnormal cells even function normally. Chronic lymphocytic leukemia is the most common leukemia among adults. The disease may take as long as 10 years to develop. This leukemia typically changes within several years into an acute leukemia that is resistant to most treatments. Chronic myeloid leukemia also occurs primarily in adults.
Cause.
The cause of most leukemia is unknown. Possible causes include genetic abnormalities and exposure to radiation or certain chemicals. In patients with chronic myeloid leukemia, sections of two chromosomes have switched places. This switch leads to the production of an enzyme that triggers cell growth. Scientists have created a drug that blocks the action of the enzyme. See Enzyme (Uses) . The drug, marketed as Gleevec, is highly effective for treating chronic myeloid leukemia. By targeting the abnormality that causes the growth of the leukemia cells, Gleevec kills only leukemia cells. As a result, side effects of the treatment are minimal. Scientists are working to identify all the molecular abnormalities of each type of leukemia so that similar treatments can be developed.
See also Blood (Blood disorders) ; Bone marrow transplant ; Chemotherapy ; Interferon .
