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Childhood Cancers: Leukaemia
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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
. 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
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