Although the cause of leukemia in most patients is unknown, several factors are associated with increased risk of developing the disease. Factors that influence risk of developing leukemia include:
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Age
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Prior Chemotherapy
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Ethnicity/Gender
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Inherited Syndromes (such as Down Syndrome)
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Ionizing Radiation
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Infection by certain viruses
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Cigarette smoking
The relative effects of these and other risk factors in any given case of cancer is variable. Some of these and other risk factors are discussed on the following pages.
Age
The risk of developing most types of leukemia increases steadily with age. The curve for acute lymphoblastic leukemia (ALL) incidence, however, is U-shaped: highest between the ages of 3-7 and rising again after the age of 40.(1) The reason for this peak in early childhood ALL remains uncertain.
More information about the relationship between cancer and age can be found in the Mutation section.
Chemotherapy
There is a subset of acute myeloid leukemia (AML), known as "secondary AML" or "therapy-related myeloid leukemia," which can develop following treatment with chemotherapy. Although a causal relationship is implied by the name, the exact mechanism remains unknown.(2)Prognosis for secondary AML is generally unfavorable compared to primary AML.(3)
Ethnicity/Gender
With the exception of chronic myeloid leukemia (CML), which has a similar incidence in whites and blacks, leukemia occurs more commonly in those of white ancestry compared to those of Asian, Hispanic and black ancestry. Leukemia also occurs more frequently in males than females.(1)
Inherited Syndromes
Children with Down syndrome (DS) have a roughly 20-fold increased risk of developing childhood leukemia compared to children without DS.(4)Approximately 10% of children with DS are born with a "transient leukemia" that resolves spontaneously within months of birth. One to two percent, however, develop a malignant acute leukemia requiring chemotherapy by the age of 4.(5) While several hypotheses have been proposed, the reason for this increased risk remains uncertain.
Other inherited syndromes that increase risk of leukemia include:
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Ataxia-telangiectasia(6)
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Bloom syndrome
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Fanconi syndrome(7)
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Klinefelter syndrome(8)
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Neurofibromatosis
Ionizing Radiation
An increase in leukemia has been observed in survivors of the atomic bombing of Japanese cities. Although the risk associated with exposure to lower level radiation is not clear, studies have shown an increase in leukemia following the use of radiotherapy for ankylosing spondylitis (a form of arthritis) and exposure to diagnostic X-rays of the fetus during pregnancy.(9)
Viruses
Infection with Human T-cell Lymphotropic Virus-1 (HTLV-I) is linked to the development of Adult T-cell Leukemia/Lymphoma (ATLL), a cancer of activated mature T lymphocytes.(10) Learn more about T lymphocytes
HTLV-I and ATLL are widespread in certain regions of the world, such as the Caribbean basin, Japan, and parts of South America and Africa, while very rare in others.(10) Most people who are infected with HTLV-I do not develop leukemia.(11) Data from cancer registries in Japan suggest the lifetime risk of developing ATLL among those infected is 2.1% for females and 6.6% for males.(12)
Although the exact mechanism by which HTLV-I infection induces cancer is not known, laboratory studies have identified several mechanisms which may be involved. (12) Learn more about viruses and cancer
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