Who gets leukemia

Acute leukemia is the most common childhood cancer. Often thought of as strictly a
childhood disease, leukemia actually afflicts many more adults than children. Each
year in the United States, approximately 3,500 children are diagnosed with acute
leukemia.
Childhood leukemia is most commonly diagnosed at ages two to seven, with the
highest incidence at approximately three years of age. In the United States, leukemia
is more common in whites than in blacks, and boys have a slightly higher incidence
than girls. Children with certain genetic diseases have a higher risk of developing
leukemia than does the general population.
Leukemia is not contagious; it cannot be passed from one person to another.
Although the exact cause of childhood leukemia is a mystery, certain factors are
known to increase the risk of developing the disease.
Genetic factors
Persons with extra chromosomes (genetic material contained in cells) or certain
chromosomal abnormalities have a greater chance of developing leukemia. Children
with Down syndrome, neurofibromatosis type 1 (NF1), Shwachman syndrome, Bloom
syndrome, Franconi anemia, Kostmann syndrome, and ataxia telangiectasia have a
higher risk of getting leukemia than do children without these genetic disorders.
However, most children with these syndromes do not develop leukemia.
In cases where one identical twin has leukemia before the age of 6, the other twin has
a 25 percent chance of developing the disease within one year. The risk for the second
twin is less if the sibling with the disease is older when diagnosed. Recent data suggest
that this high degree of risk is due to connection of the circulation (blood vessels) in
identical twins while in the womb. In fraternal (non-identical twins), there is minimal
if any increased risk of leukemia developing in both twins.
Environmental factors
Exposure to ionizing radiation and certain toxic chemicals may predispose individuals
to leukemia and other problems involving the bone marrow. Many Japanese who
were exposed to fallout from the atomic bomb during World War II and some of the
people living near the Chernobyl accident in the Ukraine have developed leukemia.
However, children exposed to irradiation from the bombs while in the mother’s
womb did not have an increased risk of developing leukemia.
Chronic exposure to benzene has been associated with leukemia in adults. Also, radi-
ation given for conditions such as tinea capitis (ringworm of the scalp) and thymus
enlargement can increase the risk of developing leukemia. Most children, however,
are not exposed to large amounts of radiation or industrial chemicals.
The data are mixed about whether exposure to electromagnetic fields increases the risk
of leukemia. Most recent data suggest that if there is an increased risk, it is minimal.
For information about the US government’s electromagnetic field (EMF) research
efforts, including public information materials developed by the EMF Research and
Public Information Dissemination (EMF RAPID) program, refer to the EMF RAPID
home page on the Internet: www.niehs.nih.gov/oc/factsheets/emf/emf.htm. Additional
information on electromagnetic fields is available at the FCC website at www.fcc.gov/oet/
rfsafety.
Certain types of chemotherapy (drugs that inhibit the enzyme topoisomerase and
alkylating agents) or radiation treatments for prior cancers can cause acute myeloid
leukemia. The greatest risk is one year after treatment with topoisomerase inhibitors
and four to five years after treatment with alkylating agents and irradiation.
Viral factors
Viruses that cause leukemia in cows, cats, chickens, gibbons, and mice have been
found. A T-cell virus has been identified that causes a rare type of leukemialymphoma
in adults; however, no virus has been found that causes the types of leukemia com-
monly found in children.
Summary
Currently, it is thought that a complex interaction among genetic, environmental,
immunologic, and possibly viral factors predisposes individuals to leukemia. One or
more of these factors causes a genetic accident (mutation) in an immature, but other-
wise normal, blood cell. This mutation prevents the cell from maturing and enables it
to divide frequently, producing more abnormal cells. The most important point for
parents to remember is that at present there is no way to predict or prevent leukemia
in children.