Acute Lymphoblastic Leukemia
(also referred to as acute lymphocytic leukemia and acute
lymphoid leukemia)
Acute lymphoblastic leukemia (ALL) is the most common form of childhood
cancer. It affects lymphocytes, a class of white blood cells. Leukemic cells
accumulate in the bone marrow, replace normal blood cells and spread to
the liver, spleen, lymph nodes, central nervous system, kidneys and gonads.
About 2,000 children are diagnosed each year in the United States. Peak
incidence occurs from ages 3 to 5 years old. The Philadelphia
Chromosome Positive aspect of Travis' diagnosis is much more rare and makes
finding a potential donor match more difficult, while also making a bone
marrow transplant one of the only treatment options as this strain does
not respond to conventional therapies which include:
Chemotherapy, treatment with anticancer drugs, is the mainstay of treatment
for leukemia. Chemotherapy is considered systemic treatment because the
drugs travel through the bloodstream and can kill cells throughout the body.
Combinations of two or more anticancer drugs may be given orally or intravenously.
Some patients receive drugs intrathecally to destroy cancer cells in the
central nervous system. Anticancer drugs are injected directly into the
cerebrospinal fluid, which surrounds the brain and the spinal cord. High-dose
chemotherapy is treatment with large doses of anticancer drugs in an effort
to kill all the leukemic cells.
Radiation therapy, the use of high-energy rays to destroy cancer cells,
also may be used to treat leukemia. Radiation therapy is a local treatment
because only cells in the treated area are damaged.
* Involved field irradiation is the use of radiation therapy to kill
cancer cells in an area of the body where they are known to be present.
This area is called the involved field.
* Total-body irradiation may be used before bone marrow transplantation
(see below) to kill leukemic cells. In this form of therapy, radiation
is generally given in multiple doses over the course of several days to
all areas of the body.
Bone marrow transplantation (BMT) is done to allow the administration
of very high doses of chemotherapy and, in some cases, to provide the leukemia
patient with disease-free bone marrow (see NCI's Research Report: Bone Marrow
Transplantation). Marrow for transplantation can be obtained in three ways
and is described by its source: another person (allogeneic), an identical
twin (syngeneic), or the patient (autologous).
To prepare for BMT, patients receive large doses of drugs and/or radiation
in an effort to destroy all leukemic cells. Dosages are so great that the
patient's own bone marrow is destroyed, and the patient is totally dependent
upon supportive care for control of bleeding and defense against infection.
In allogeneic transplantation, marrow is taken from a matched donor and
infused into the patient's bloodstream. The donated cells travel from the
blood to the bone marrow where, in time, they usually become functioning
marrow.
The success of allogeneic BMT depends partly upon how closely the donor's
marrow genetically matches the recipient's marrow. Matching bone marrow
involves comparing six characteristic proteins - markers called human leukocyte
antigens (HLAs) - on the surface of white blood cells. The more closely
the donor's HLAs match the patient's, the greater the chance of successful
transplantation. Matching is also important to reduce the chance that the
patient's body will reject the donor's marrow. The only perfect HLA match
is between identical twins. The next best choice is between close relatives,
such as siblings.
Matching also is important to decrease the risk of graft-versus-host
disease (GVHD), a major complication of allogeneic BMT. In this disease,
the donated marrow reacts against the patient's body. Although mild GVHD
may be beneficial in some patients (because the donor's cells can destroy
leukemic cells that remain in the body), severe GVHD is potentially fatal.
In spite of improved matching techniques, GVHD is not uncommon. Currently,
studies are in progress to find techniques that will help prevent GVHD.
Because the patient's own bone marrow is used, autologous bone marrow
transplantation eliminates the risk of GVHD. During remission, marrow is
removed, frozen, and stored for reinfusion should the patient relapse. To
be sure any undetectable leukemic cells that may remain in the patient's
marrow are destroyed, the marrow removed from the patient must be treated
in a process called purging. Researchers continue to look for more effective
methods of purging and better ways to prepare patients for BMT. Therapy
using BMT for leukemia patients with advanced, resistant disease has not
been successful. Use of BMT earlier in the treatment plan has been more
effective. |