Leukemia is a
that starts in the organs that make blood, namely the bone marrow and the
lymph system. Depending on their characteristics, leukemias can be divided
into two broad types. Acute leukemias are the rapidly progressing
leukemias, while the
progress more slowly. The vast majority of the childhood leukemias are of
the acute form.
The cells that make up blood are produced in the bone marrow and the lymph
system. The bone marrow is the spongy tissue found in the large bones of
the body. The lymph system includes the spleen (an organ in the upper
abdomen), the thymus (a small organ beneath the breastbone), and the
tonsils (an organ in the throat). In addition, the lymph vessels (tiny
tubes that branch like blood vessels into all parts of the body) and lymph
nodes (pea-shaped organs that are found along the network of lymph
vessels) are also part of the lymph system. Lymph is a milky fluid that
contains cells. Clusters of lymph nodes are found in the neck, underarm,
pelvis, abdomen, and chest.
Blood is made up of red blood cells (RBCs), which carry oxygen and other
materials to all tissues of the body; white blood cells (WBCs), which
fight infection; and platelets, which play a part in the clotting of the
blood. The white blood cells can be further subdivided into three main
types: granulocytes, monocytes, and lymphocytes.
The granulocytes, as their name suggests, contain particles (granules).
These granules contain special proteins (enzymes) and several other
substances that can break down chemicals and destroy microorganisms, such
as bacteria. Monocytes are the second type of white blood cell. They are
also important in defending the body against pathogens.
The lymphocytes form the third type of white blood cell. There are two
main types of lymphocytes: T lymphocytes and B lymphocytes. They have
different functions within the immune system. The B cells protect the body
by making antibodies, which are proteins that can attach to the surfaces
of bacteria and viruses. This attachment sends signals to many other cell
types to come and destroy the antibody-coated organism. The T cells
protect the body against viruses. When a virus enters a cell, it produces
certain proteins that are projected onto the surface of the infected cell.
The T cells recognize these proteins and make certain chemicals that are
capable of destroying the virus-infected cells. In addition, the T cells
can destroy some types of cancer cells.
The bone marrow makes stem cells, which are the precursors of the
different blood cells. These stem cells mature through stages into RBCs,
WBCs, or platelets. In acute leukemias, the maturation process of the
white blood cells is interrupted. The immature cells (blasts) proliferate
rapidly and begin to accumulate in various organs and tissues, thereby
affecting their normal function. This uncontrolled proliferation of the
immature cells in the bone marrow affects the production of the normal red
blood cells and platelets as well.
Acute leukemias are of two types: acute lymphocytic leukemia and acute
myelogenous leukemia. Different types of white blood cells are involved in
the two leukemias. In acute lymphocytic leukemia (ALL), it is the T or the
B lymphocytes that become cancerous. The B cell leukemias are more common
than T cell leukemias. Acute myelogenous leukemia, also known as acute
nonlymphocytic leukemia (ANLL), is a cancer of the monocytes and/or
Leukemias account for 2 percent of all cancers. Because leukemia is the
most common form of childhood cancer, it is often regarded as a disease of
childhood. However, leukemias affect nine times as many adults as
children. Half of the cases occur in people who are 60 years of age or
older. The incidence of acute and chronic leukemias is about the same.
Leukemia strikes both sexes and all ages. The human T-cell leukemia virus
(HTLV-I) is believed to be the causative agent for some kinds of
leukemias. However, as of 2004, the cause of most leukemias is not known.
Acute lymphoid leukemia (ALL) is more common among Caucasians than among
African-Americans, while acute myeloid leukemia (AML) affects both races
equally. The incidence of acute leukemia is slightly higher among men than
women. People with Jewish ancestry have a higher likelihood of getting
leukemia. A higher incidence of leukemia has also been observed among
and some other genetic abnormalities.
Causes and symptoms
Exposure to ionizing radiation and to certain organic chemicals, such as
benzene, is believed to increase the risk of developing leukemia. Having a
history of diseases that damage the bone marrow, such as aplastic anemia,
or a history of cancers of the lymphatic system puts people at a high risk
for developing acute leukemias. Similarly, the use of anticancer
medications, immunosuppressants, and the antibiotic chloramphenicol are
also considered risk factors for developing acute leukemias.
The symptoms of leukemia are generally vague and non-specific. A patient
may experience all or some of the following symptoms:
Like all cancers, acute leukemias are most successfully treated when found
early. There were as of 2004 no screening tests available.
If the doctor has reason to suspect leukemia, he or she will conduct a
very thorough physical examination to look for enlarged lymph nodes in the
neck, underarm, and pelvic region. Swollen gums, enlarged liver or spleen,
, or pinpoint red
all over the body are some of the signs of leukemia. Urine and blood
tests may be ordered to check for microscopic amounts of blood in the
urine and to obtain a complete differential blood count. This count gives
the numbers and percentages of the different cells found in the blood. An
abnormal blood test might suggest leukemia; however, the diagnosis has to
be confirmed by more specific tests.
The doctor may perform a bone marrow biopsy to confirm the diagnosis of
leukemia. During the biopsy, a cylindrical piece of bone and marrow is
removed. The tissue is generally taken out of the hipbone. These samples
are sent to the laboratory for examination. In addition to diagnosis, the
biopsy is also repeated during the treatment phase of the disease to see
if the leukemia is responding to therapy.
A spinal tap (lumbar puncture) is another procedure that the doctor may
order to diagnose leukemia. In this procedure, a small needle is inserted
into the spinal cavity in the lower back to withdraw some cerebrospinal
fluid and to look for leukemic cells.
Standard imaging tests, such as x rays,
scans (CT scans), and
magnetic resonance imaging
(MRI) may be used to check whether the leukemic cells have invaded other
areas of the body, such as the bones, chest, kidneys, abdomen, or brain. A
gallium scan or bone scan is a test in which a radioactive chemical is
injected into the body. This
An enhanced transmission electron microscopy (TEM) image of white
blood cells from a patient with acute myelogenous leukemia cells.
(© Professor Aaron Polliack, Science Source/Photo Researchers,
chemical accumulates in the areas of cancer or infection, allowing them
to be viewed with a special camera.
—A special protein made by the body's immune system as a
defense against foreign material (bacteria, viruses, etc.) that enters
the body. It is uniquely designed to attack and neutralize the specific
antigen that triggered the immune response.
—The surgical removal and microscopic examination of living
tissue for diagnostic purposes or to follow the course of a disease.
Most commonly the term refers to the collection and analysis of tissue
from a suspected tumor to establish malignancy.
—Any treatment of an illness with chemical agents. The term is
usually used to describe the treatment of cancer with drugs that inhibit
cancer growth or destroy cancer cells.
Computed tomography (CT)
—An imaging technique in which cross-sectional x rays of the body
are compiled to create a three-dimensional image of the body's
internal structures; also called computed axial tomography.
—Chemicals made by the cells that act on other cells to stimulate
or inhibit their function. They are important controllers of immune
—A mode of cancer treatment in which the immune system is
stimulated to fight the cancer.
—A procedure in which the doctor inserts a small needle into the
spinal cavity in the lower back to withdraw spinal fluid for testing.
Also known as a spinal tap.
Magnetic resonance imaging (MRI)
—An imaging technique that uses a large circular magnet and radio
waves to generate signals from atoms in the body. These signals are used
to construct detailed images of internal body structures and organs,
including the brain.
—The process by which stem cells transform from immature cells
without a specific function into a particular type of blood cell with
—A cancer treatment that uses high-energy rays or particles to
kill or weaken cancer cells. Radiation may be delivered externally or
internally via surgically implanted pellets. Also called radiotherapy.
—A disappearance of a disease and its symptoms. Complete
remission means that all disease is gone. Partial remission means that
the disease is significantly improved, but residual traces of the
disease are still present. A remission may be due to treatment or may be
Like all cancers, the prognosis for leukemia depends on the
patient's age and general health. According to statistics,
more than 60 percent of the patients with leukemia survive for at least a
year after diagnosis. Acute myelocytic leukemia (AML) has a poorer
prognosis rate than acute lymphocytic leukemias (ALL) and the chronic
leukemias. Between 1985 and 2004, the five-year survival rate for patients
with ALL increased from 38 to 57 percent.
Interestingly enough, since most childhood leukemias are of the ALL type,
chemotherapy has been highly successful in their treatment. This is
because chemotherapeutic drugs are most effective against actively growing
cells. Due to the new combinations of anticancer drugs being used, the
survival rates among children with ALL have improved dramatically. Eighty
percent of the children diagnosed with ALL as of 2004 survive for five
years or more, as compared to 50 percent in the late 1970s.
Most cancers can be prevented by changes in lifestyle or diet, which will
reduce the risk factors. However, in leukemias, there are as of 2004 no
such known risk factors. Therefore, as of 2004, no way is known to prevent
leukemias from developing. People who are at an increased risk for
developing leukemia because of proven exposure to ionizing radiation or
exposure to the toxic liquid benzene, and people with Down syndrome,
should undergo periodic medical checkups.
Parents of a child with leukemia must balance their own fears for their
child's health with the child's fears and worries. Also,
given the large financial burden leukemia treatment entails, parents will
want to make sure they are aware of what and what is not covered by their
insurance. Parents can find a variety of sources, written and online, that
will help them deal with the new circumstances of themselves and their
Campana, Dario, and Ching-Hon Pui. "Childhood Leukemia." In
Edited by Martin D. Abeloff. London: Churchill Livingstone, 2000.
Thompson, George H. "The Neck." In
Nelson Textbook of Pediatrics.
Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.
Tubergen, David G., and Archie Bleyer. "The Leukemias." In
Nelson Textbook of Pediatrics.
Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.
American Cancer Society.
1599 Clifton Rd., NE, Atlanta, GA 30329–4251. Web site:
Cancer Research Institute.
681 Fifth Ave., New York, NY 10022. Web site:
Leukemia Society of America Inc.
600 Third Ave., New York, NY 10016. Web site:
National Cancer Institute.
Building 31, Room 10A31, 31 Center Drive, MSC 2580, Bethesda, MD