(
Cáncer infantil: Leucemia
)
About Leukemia
The term leukemia refers to cancers of the white blood cells,
which are also referred to as
leukocytes
or
WBC
s. When a child has leukemia, large numbers of abnormal white blood
cells are produced in the bone marrow. These abnormal white cells
crowd the bone marrow and flood the bloodstream, but they cannot
perform their proper role of protecting the body against disease
because they are defective.
As leukemia progresses, the cancer interferes with the
body's production of other types of blood cells, including red
blood cells and platelets. This results in
anemia
(low numbers of red cells) and bleeding problems, in addition to
the increased risk of infection caused by white cell
abnormalities.
As a group, leukemias account for about 25% of all childhood
cancers and affect about 2,200 American young people each year.
Luckily, the chances for a cure are very good with leukemia. With
treatment, most children with leukemia are free of the disease
without it coming back.
Types of Leukemia
In general, leukemias are classified into
acute
(rapidly developing) and
chronic
(slowly developing) forms. In children, about 98% of leukemias are
acute.
Acute childhood leukemias are also divided into
acute lymphocytic leukemia
(ALL) and
acute myelogenous leukemia
(AML), depending on whether specific white blood cells called
lymphyocytes
(or
myelocytes
), which are linked to immune defenses, are involved.
Approximately 60% of children with leukemia have ALL, and about
38% have AML. Although slow-growing
chronic myelogenous leukemia
(CML) may also be seen in children, it is very rare, accounting for
fewer than 50 cases of childhood leukemia each year in the United
States.
Causes
The ALL form of the disease most commonly occurs in younger
children ages 2 to 8, with a peak incidence at age 4. But it can
affect all age groups.
Children have a 20% to 25% chance of developing ALL or AML if
they have an identical twin who was diagnosed with the illness
before age 6. In general, nonidentical twins and other siblings of
children with leukemia have two to four times the average risk of
developing this illness.
Children who have inherited certain genetic problems - such as
Li-Fraumeni syndrome, Down syndrome, Kleinfelter syndrome,
neurofibromatosis
, ataxia telangectasia, or Fanconi's anemia - have a higher
risk of developing leukemia, as do children who are receiving
medical drugs to suppress their immune systems after organ
transplants.
Children who have received prior radiation or chemotherapy for
other types of cancer also have a higher risk for leukemia, usually
within the first 8 years after treatment.
In most cases, neither parents nor children have control over
the factors that trigger leukemia, although current studies are
investigating the possibility that some environmental factors may
predispose a child to develop the disease. Most leukemias arise
from noninherited mutations (changes) in the genes of growing blood
cells. Because these errors occur randomly and unpredictably, there
is currently no effective way to prevent most types of
leukemia.
To limit the risk of prenatal radiation exposure as a trigger
for leukemia (especially ALL), women who are pregnant or who
suspect that they might be pregnant should always inform their
doctors before undergoing tests or medical procedures that involve
radiation (such as X-rays).
Regular checkups can spot early symptoms of leukemia in the
relatively rare cases where this cancer is linked to an inherited
genetic problem, to prior cancer treatment, or to use of
immunosuppressive drugs for organ transplants.
Symptoms
Because infection-fighting white blood cells are defective in
children with leukemia, these children may experience increased
episodes of
fevers
and infections.
They may also become anemic because leukemia affects the bone
marrow's production of oxygen-carrying red blood cells. This
makes them appear pale, and they may become abnormally tired and
short of breath while playing.
Children with leukemia may also bruise and bleed very easily,
experience frequent nosebleeds, or bleed for an unusually long time
after even a minor cut because leukemia destroys the bone
marrow's ability to produce clot-forming platelets.
Other symptoms of leukemia may include:
- pain in the bones or joints, sometimes causing a limp
- swollen lymph nodes (sometimes called swollen glands) in the
neck, groin, or elsewhere
- an abnormally tired feeling
- poor appetite
In about 12% of children with AML and 6% of children with ALL,
spread of leukemia to the brain causes
headaches
, seizures, balance problems, or abnormal
vision
. If ALL spreads to the lymph nodes inside the chest, the enlarged
gland can crowd the trachea (windpipe) and important blood vessels,
leading to breathing problems and interference with blood flow to
and from the heart.
Diagnosis
Your child's doctor will perform a physical examination to
check for signs of infection, anemia, abnormal bleeding, and
swollen lymph nodes. The doctor will also feel your child's
abdomen to see if there is an enlarged liver or spleen because they
can become enlarged with some cancers in children. In addition to
doing a physical examination, the doctor will ask you about any
concerns and symptoms you have, your past health, your family's
health, any medications you're taking, any allergies you may
have, and other issues. This is called the medical history.
After this exam, the doctor will order a CBC (complete blood
count) to measure the numbers of white cells, red cells, and
platelets in your child's blood. A blood smear will also be
examined under a microscope to check for certain specific types of
abnormal blood cells that are typically seen in patients with
leukemia. Blood chemistries will also be checked.
Then, depending on the results of your child's physical exam
and preliminary blood tests, your child may need the following:
- a bone marrow biopsy and aspiration, in which marrow samples
are removed from the body (usually from the back of the hip) for
testing
- a lymph node biopsy, in which lymph nodes are removed and
examined under a microscope to look for abnormal cells
- a
lumbar puncture
(spinal tap), where a sample of spinal fluid is removed from the
lower back and examined for evidence of abnormal cells. This will
show whether the leukemia has spread to the
central nervous system
(brain and spinal cord).
Bone marrow or lymph node samples will be examined and
additional testing will be done to determine the specific type of
leukemia. In addition to these basic lab tests, cell evaluations
are also generally done, including genetic studies to distinguish
between specific types of leukemia, as well as certain features of
the leukemia cells. Children will receive anesthesia or sedative
medications for any painful procedures.
Treatment
Certain features of a child's leukemia, such as age and
initial white blood cell count, are used in determining the
intensity of treatment needed to achieve the best chance for cure.
Although all children with ALL are treated with chemotherapy, the
dosages and drug combinations may differ.
To decrease the chance that leukemia will invade the child's
central nervous system, patients receive intrathecal chemotherapy,
the administration of cancer-killing drugs into the cerebrospinal
fluid around the brain and spinal cord. Radiation treatments, which
use high-energy rays to shrink tumors and keep cancer cells from
growing, may be used in addition to intrathecal chemotherapy for
certain high-risk patients. Children then require continued close
monitoring by a pediatric oncologist, a specialist in childhood
cancer.
After treatment begins, the goal is
remission
of the leukemia (when there is no longer evidence of cancer cells
in the body). Once remission has occurred, maintenance chemotherapy
is usually used to keep the child in remission. Maintenance
chemotherapy is given in cycles over a period of 2 to 3 years to
keep the cancer from reoccurring. Leukemia will almost always
relapse (reoccur) if this additional chemotherapy isn't given.
Sometimes the cancer will return in spite of maintenance
chemotherapy, and other forms of chemotherapy will then be
necessary.
Sometimes a bone marrow transplant may be necessary in addition
to - or instead of - chemotherapy, depending on the type of
leukemia a child has. During a bone marrow transplant, healthy bone
marrow is introduced into a child's body.
Intensive leukemia chemotherapy have certain side effects,
including hair loss, nausea and vomiting in the short term, and
potential health problems down the line. As your child is treated
for leukemia, your child's cancer treatment team will monitor
the child closely for those side effects.
But with the proper treatment, the outlook for kids who are
diagnosed with leukemia is quite good. Some forms of childhood
leukemia have a remission rate of up to 90%; all children then
require regular maintenance chemotherapy and other treatment to
continue to be cancer-free. Overall cure rates differ depending on
the specific features of a child's disease. Most childhood
leukemias have very high remission rates. And the majority of
children can be cured - meaning that they are in permanent
remission - of the disease.
Updated and reviewed by:
Robin E. Miller, MD
Date reviewed: June 2007
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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