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About 3,830 new cases of acute lymphocytic leukemia (ALL) are diagnosed
each year in the United States. It is the most common type of leukemia under
the age of 19. Children are most likely to develop the disease, but it can
occur at any age. Acute lymphocytic leukemia may be called by several names,
including acute lymphoid leukemia and acute lymphoblastic leukemia.
ALL results from an acquired (not inherited) genetic injury to the DNA of a
single cell in the bone marrow. The disease is often referred to as acute
lymphoblastic leukemia because the leukemic cell that replaces the normal
marrow is the (leukemic) lymphoblast. The effects are: 1) the uncontrolled
and exaggerated growth and accumulation of cells called "lymphoblasts" or "leukemic
blasts," which fail to function as normal blood cells and 2) the blockade of
the production of normal marrow cells, leading to a deficiency of red cells
(anemia), platelets (thrombocytopenia), and normal white cells (especially
neutrophils, i.e., neutropenia) in the blood.
Causes and Risk Factors
In most cases, the cause of acute lymphocytic leukemia is not evident. Few
factors have been associated with an increased risk of developing the
disease. Exposure to high doses of irradiation, as carefully studied in the
Japanese survivors of atomic bomb detonations, is one such factor. Unlike
other forms of leukemia, acute lymphocytic leukemia occurs at different
rates in different locations. There are higher leukemia rates in more
developed countries and in higher socioeconomic groups.
The current causes of acute lymphoblastic leukemia in children or adults
are not known. Scientists continue to explore possible relationships with
life-style or environmental factors but no firm conclusions have yet been
reached. Given the amount of study, this suggests that multifaceted complex
factors may be involved. It is extremely disconcerting to patients and their
families to wonder what they may have done differently to avoid the disease.
Unfortunately, at the present time there is no known way to prevent the
disease. Acute lymphocytic leukemia occurs most often in the first decade of
life but increases in frequency again in older individuals.
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Subtypes of Acute
Lymphocytic Leukemia
Acute lymphocytic leukemia can develop from primitive lymphocytes that are
in various stages of development. The principal subtypes are uncovered by
special tests on the leukemic lymphoblasts called "immunophenotyping."
Phenotype is the physical characteristics of the cells and these are
measured using immune tools. The subclassification of cell types is
important since it helps to determine the best treatment to apply in each
type of leukemia. The principle subtypes are T lymphocyte and B lymphocyte
types, so named because the cell has features that are similar to normal T
or B lymphocytes. In addition, the B cell type can be divided into a
precursor B cell type, as well. Once these features are determined the term
used may be acute T lymphoblastic leukemia or acute precursor (or pre) B
cell lymphoblastic leukemia. Other markers on the lymphoblasts that can be
detected with immunophenotyping and may be useful to the physician include
the common acute lymphoblastic leukemia antigen, cALLa, now called CD 10.
Immunophenotypes
B lymphocytic lineage subtypes. These cases are identified by finding
cell surface markers on the leukemic blast cells that are identical to those
that develop on normal B lymphocytes. About 85 percent of cases are of the
precursor B or B cell subtype.
T lymphocytic lineage subtypes. These cases are identified by finding
cell surface markers on the leukemic blast cells that are identical to those
that develop in normal T lymphocytes. About 15 percent of cases are of the T
cell subtype.
Chromosome Abnormalities
Injury to chromosomes can be assessed by cytogenetic methods, and the
specific alteration in chromosomes also aids in subclassifying acute
lymphocytic leukemia. For example, a change in chromosome number 22,
referred to as the Philadelphia or Ph chromosome, which occurs in a small
percentage of children and a larger percentage of adults with acute
lymphocytic leukemia, places the patient in a highter risk category. Thus,
the approach to therapy would be intensified in those subsets of patients.
Symptoms and Signs
Most patients feel a loss of well-being. They tire more easily and may
feel short of breath when physically active. They may have a pale complexion
from anemia. Signs of bleeding because of a very low platelet count may be
noticed. These include black-and-blue marks occurring for no reason or
because of a minor injury, the appearance of pinhead-sized, red spots under
the skin, called petechiae, or prolonged bleeding from minor cuts.
Discomfort in the bones and joints may occur. Fever in the absence of an
obvious cause is common. Leukemic lymphoblasts may accumulate in the
lymphatic system, and the lymph nodes can become enlarged. The leukemia
cells can also collect on the lining of the brain and spinal cord and lead
to headache or vomiting.
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Approach to Diagnosis
- Medical history and physical examination
- Complete blood counts
- Bone marrow examination
- Cytogenetics
- Immunophenotyping
To diagnose the disease, the blood and marrow cells must be examined. In
addition to low red cell and platelet counts, examination of the stained
(dyed) blood cells with a light microscope will usually show the presence of
leukemic blast cells. This is confirmed by examination of the marrow which
almost always shows leukemia cells. The blood and/or marrow cells are also
used for studies of the number and shape of chromosomes (cytogenetic
examination), immunophenotyping, and other special studies, if required.
Blood and bone marrow samples are used to diagnose and classify the
disease. The following tests are used in the further classification of the
disease. Examination of leukemic cells by cytogenetic techniques permits
identification of chromosomes or gene abnormalities in the cells. The
immunophenotype and chromosome abnormalities in the leukemic cells are very
important guides in determining the approach to treatment and the intensity
of the drug combinations to be used.
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Immunophenotyping
This is a laboratory test that enable the physician to determine the type of
disease that is present in the patient. It uses the antigens (proteins) on
the cell surface and the antibodies produced by the body that match the
antigen.
A method that uses the reaction of antibodies with cell antigens to
determine a specific type of cell in a sample of blood cells, marrow cells,
or lymph node cells. The antibodies react with specific antigens on the
cell. A tag is attached to an antibody so that it can be detected. The tag
can be identified by the laboratory equipment used for the test. As cells
carrying their array of antigens are tagged with specific antibodies they
can be identified; for example, myelogenous leukemic cells can be
distinguished from lymphocytic leukemic cells. Normal lymphocytes may be
distinguished from leukemic lymphocytes. This method also helps to
subclassify cell types, which may, in turn, help to decide on the best
treatment to apply in that type of leukemia or lymphoma. The antigen on a
cell is referred to as cluster of differentiation or "CD" with an associated
number. For example, CD7 and 19 may be present on leukemic lymphoblasts and
CD13 and 33 on leukemic myeloblasts.
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Cytogenetic Examination
Cytogenetic examination of tissue is the process of analyzing the number and
shape of the chromosomes of cells. The individual, who prepares, examines
and interprets the number and shape of chromosomes in cells is called a
cytogeneticist. In addition to identifying chromosome alterations, the
specific genes affected can be identified in some cases. These findings are
very helpful in diagnosing specific types of leukemia and lymphoma, in
determining treatment approaches, and in following the response to
treatment.
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Get More
Information
The Leukemia & Lymphoma Society offers ongoing education programs
featuring leading leukemia specialists discussing the latest issues in the
diagnosis and treatment of leukemia. Visit the
Leukemia Education
Series page to find out about upcoming and archived
programs. These programs are offered at no charge.
Further details of treatment and supportive
care and the beneficial and adverse effects of treatment may be obtained
from the Society's informational booklet on acute lymphocytic leukemia. Read
or order online the Society's free publication
Acute
Lymphocytic Leukemia.
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Contact
The Leukemia & Lymphoma Society
1311 Mamaroneck Ave.
White Plains, NY 10605
or call the
Information Resource Center at (800) 955-4572.
Helpful Links
- National Cancer Institute
This site offers comprehensive information about cancers and the
diagnosis procedures.
- Medicine Online
This site offers information about diagnosis and treatment
(including immunotherapy), with pages written by several
physicians. Go to "cancer links/leukemia/current" .
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