Childhood Cancers: Leukaemia

Description

Leukaemia refers to any of several types of cancers that affect blood cells, including oxygen-carrying red cells; certain infection-fighting white cells, such as granulocytes, macrophages and lymphocytes; and platelets, which aid in blood clotting.

According to the American Cancer Society , leukaemia is the sixth leading cause of cancer deaths among men and the seventh leading cause of cancer deaths among women. It accounts for about one-third of all cancer deaths in children. Over 28,500 new cases of leukaemia are diagnosed in the United States each year. Blood cells are made in the bone marrow, the spongy tissue in the centre of bones. A leukaemia begins when an immature blood cell in the marrow, known as a progenitor cell, becomes cancerous, dividing uncontrollably and overriding the body's normal restrictions on cell division. Over time, the marrow becomes crowded with cancerous cells, all of them descendants of the first abnormal cell. The malignant cells may also accumulate in a patient's lymph nodes, spleen, and elsewhere. At the time of diagnosis, up to a trillion leukaemic cells may be present in the body. The mass of leukaemic cells in the marrow suppresses the production of healthy blood cells, giving rise to the symptoms typical of leukaemia. Hence the term itself, which is Greek for white blood ( leukos , "white"; haima , "blood") was applied to the disease.

The causes of most types of leukaemia are unknown but 4 known causes of certain types of leukaemia have been identified. These are:

• Intensive radiation exposure or moderately intense exposure for long periods.
• Exposure to certain chemicals can also cause leukaemia. Workers exposed to benzene over long periods have an increased risk of developing acute myelocytic leukaemia. Chemotherapy drugs used to treat breast cancer, ovarian cancer, lymphomas, and certain other cancers also increase a patient's risk of later developing acute myelocytic leukaemia.
• Two viruses , human T-cell leukaemia viruses (HTLV) I and II, are known to cause T-cell leukaemia, a very rare form of lymphocytic leukaemia, in humans. However, only a small percentage of people who are infected with these viruses develop cancer. Although virus-related leukaemia is rare in humans, it is quite common in other animal species, such as cats, chickens, and mice.
• Genetic factors may also contribute to the development of leukaemia. Some inherited conditions, such as Down syndrome, increase a person's risk of developing leukaemia.

Symptoms and Signs

Pale skin, fatigue, and shortness of breath are signs of anaemia . Nose bleeds, gum bleeding, a tendency to bruise easily, and pinhead-sized red spots on the skin reflect the decrease in the concentration of platelets in the blood. A lack of functional white cells makes patients with leukaemia prone to infection.

Diagnosis and Treatment

Bone marrow biopsy and blood tests that monitor blood cell (generally heightened white blood cell and lowered red blood cell counts) are the primary techniques used to diagnose leukaemia. Tests such as chest X rays and examination of the spinal fluid for leukaemic cells can help doctors determine how far the disease has spread. Treatment of leukaemia depends on the type and extent of the disease and is tailored to each individual patient. The main types of treatment in use are:

• Chemotherapy is the most common treatment used. Antibiotics and transfusions of red cells and platelets help sustain patients whose blood counts are dangerously low because they are receiving intensive chemotherapy.
• Radiation may also be used to shrink collections of leukaemic cells that accumulate in various parts of the body, such as on the lining of the brain and spinal cord in acute lymphocytic leukaemia, or within lymph nodes in chronic lymphocytic leukaemia.
• Stem cell transplantation may also be performed if it is thought that chemotherapy alone is not enough or if the patient suffers a relapse. In this procedure, very intensive total body radiation or very high doses of chemotherapy or both are used. The chemotherapy and radiation are designed to destroy all the leukaemic cells in a patient's body; however, this treatment also destroys the blood-forming system in the patient's bone marrow. For this reason, healthy stem cells, the cells in bone marrow that enable long-term formation of blood, must then be infused into a patient to replenish the blood-forming system. The stem cells must come from an immunologically matched donor, usually a sibling or other close relative.
• Immunotherapy , though still in the experimental stages, is a promising new approach to treating leukaemia. In this technique, highly specific molecules known as monoclonal antibodies are manufactured in the laboratory to target molecules on the surface of leukaemic cells. The antibodies are attached to a radioactive substance, then injected intravenously into a patient. This method provides a convenient means of delivering the radioactive substance directly to leukaemic cells, where it may kill these cells with minimal effect on healthy cells.

The information in this page is presented in summarised form and has been taken from the following source(s):
1. Microsoft® Encarta® Online Encyclopaedia, ©1997-2000 Microsoft Corporation. All rights reserved. 2000: http://encarta.msn.com