Leukemia is a kind of cancer in which abnormal white blood cells grow in an uncontrolled manner. These abnormal cells interfere with the production of normal white blood cells, which fight infection. Leukemia is a disease of the bone marrow and other blood-forming organs. Consequently, leukemia also affects the production of red blood cells, which carry oxygen from the lungs throughout the body, and platelets, blood cells that help stop bleeding. Signs of leukemia include repeated infection, anemia, and frequent bleeding. 2. The cause of most human leukemia is unknown. Researchers have discovered a leukemia virus in cats, and they have identified a virus that appears to cause a rare type of leukemia in people. Other possible causes include exposure to radiation and harmful chemicals. 3. Doctors classify leukemia according to the type of white blood cell affected. Two of the main blood cell types affected by. leukemia are myeloid and lymphoid. Myeloid cells fight bacterial infections. Lymphoid cells detect and respond to the presence of foreign substances in the body. All kinds of leukemia can be either acute of chronic. 4. Acute leukemias often develop suddenly. Abnormal, immature white blood cells multiply rapidly, and the number of normal cells decreases sharply. Acute myeloid leukemia most often occurs among adults. The treatment for this leukemia is chemotherapy, the use of chemicals that are more toxic to cancer cells than to normal cells. Seventy percent of patients enter remission. During remission, the blood cells and the bone marrow temporarily return to normal. Researchers are trying to develop methods of prolonging remission in acute myeloid leukemia patients. The treatment of acute leukemias is 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. 5. Chronic leukemias develop more slowly than acute leukemias. In chronic leukemias, the abnormal white blood cells appear mature, and they resemble normal white blood cells. In the early stages of the disease, these abnormal cells even function normally to some extent. Chronic lymphocytic leukemia is the most common leukemia among adults. The average age of people suffering from this disease is the early 70's. The disease may take as long as 10 years to develop completely. Chronic myeloid leukemia is a less common form. of leukemia that occurs primarily among adults. Doctors generally use drugs to treat chronic leukemia patients.