Risk Factors for Childhood Leukemia

A risk factor is anything that affects a person’s chance of getting a disease such as cancer. Different cancers have different risk factors.

In general, leukemia is more common in boys than girls. The reason for this is not clear.  Lifestyle-related risk factors such as tobacco use, diet, body weight, and physical activity play a major role in many adult cancers. But these factors usually take many years to influence cancer risk, and they are not thought to play much of a role in childhood cancers, including leukemias.

Genetic risk factors

Genetic risk factors are those that are part of our DNA (the substance that makes up our genes). They are often inherited from our parents. While some genetic factors increase the risk of childhood leukemia, most leukemias are not linked to any known genetic causes.

Genetic syndromes

Some genetic disorders increase a child’s risk of developing leukemia:

• Down syndrome (trisomy 21): Children with Down syndrome have an extra (third) copy of chromosome 21. They are many times more likely to develop either acute lymphocytic leukemia (ALL) or acute myeloid leukemia (AML) than are other children, with an overall risk of about 2% to 3%. Down syndrome has also been linked with transient leukemia (also known as transient myeloproliferative disorder) – a leukemia-like condition within the first month of life, which often resolves on its own without treatment.
• Li-Fraumeni syndrome: This is a rare inherited condition caused by a change in the TP53 gene. People with this change have a higher risk of developing several kinds of cancer, including leukemia, bone or soft tissue sarcomas, breast cancer, adrenal gland cancer, and brain tumors.

Other genetic disorders (such as neurofibromatosis and Fanconi anemia) also carry an increased risk of leukemia, as well as some other types of cancers.

Inherited immune system problems

Certain inherited conditions cause children to be born with immune system problems. These include:

• Ataxia-telangiectasia
• Wiskott-Aldrich syndrome
• Bloom syndrome
• Shwachman-Diamond syndrome

Along with an increased risk of getting serious infections from reduced immune defenses, these children might also have an increased risk of leukemia.

Having a brother or sister with leukemia

Siblings (brothers and sisters) of children with leukemia have a slightly increased chance of developing leukemia, but the overall risk is still low. The risk is much higher among identical twins. If one twin develops childhood leukemia, the other twin has about a 1 in 5 chance of getting leukemia as well. This risk is much higher if the leukemia develops in the first year of life.

Having a parent who develops leukemia as an adult does not seem to raise a child’s risk of leukemia.

Lifestyle-related risk factors

Lifestyle-related risk factors for some adult cancers include smoking, being overweight, drinking too much alcohol, and getting too much sun exposure. These types of factors are important in many adult cancers, but they are unlikely to play a role in most childhood cancers.

Some studies have suggested that a woman drinking a lot of alcohol during pregnancy might increase the risk of leukemia in her child, but not all studies have found such a link.

Environmental risk factors

Environmental risk factors are influences in our surroundings, such as radiation and certain chemicals, that increase the risk of getting diseases such as leukemias.

Radiation exposure

Exposure to high levels of radiation is a risk factor for childhood leukemia. Japanese atomic bomb survivors had a greatly increased risk of developing AML. If a fetus is exposed to radiation within the first months of development, there may also be an increased risk of childhood leukemia, but the extent of the risk is not clear.

The possible risks from fetal or childhood exposure to lower levels of radiation, such as from x-ray tests or CT scans, are not known for sure. Some studies have found a slight increase in risk, while others have found no increased risk. Any risk increase is likely to be small, but to be safe, most doctors recommend that pregnant women and children not get these tests unless they are absolutely needed.

Exposure to chemotherapy and certain other chemicals

Children and adults treated for other cancers with certain chemotherapy drugs have a higher risk of getting a second cancers, usually AML, later in life. Drugs such as cyclophosphamide, doxorubicin, etoposide, and teniposide have been linked to a higher risk of leukemia. These leukemias usually develop within 5 to 10 years of treatment, and they tend to be hard to treat.

Exposure to chemicals such as benzene (a solvent used in the cleaning industry and to manufacture some drugs, plastics, and dyes) may cause acute leukemia in adults and, rarely, in children. Chemical exposure is more strongly linked to an increased risk of AML than to ALL.

Several studies have found a possible link between childhood leukemia and household exposure to pesticides, either during pregnancy or early childhood. Some studies have also found a possible increased risk among mothers with workplace exposure to pesticides before their child is born. However, most of these studies had serious limitations in the way they were done. More research is needed to try to confirm these findings and to provide more specific information about the possible risks.

Immune system suppression

Children who are getting intensive treatment to suppress their immune system (mainly children who have had organ transplants) have an increased risk of certain cancers, such as lymphoma and ALL.

Uncertain, unproven, or controversial risk factors

Other factors that have been studied for a possible link to childhood leukemia include:

• Exposure to electromagnetic fields (such as living near power lines)
• Living near a nuclear power plant
• Infections (especially from viruses) early in life
• Mother’s age when child is born
• Parent’s smoking history
• Fetal exposure to hormones such as diethylstilbestrol (DES) or birth control pills
• Father’s workplace exposure to chemicals and solvents
• Chemical contamination of ground water

So far, most studies have not found strong links between any of these factors and childhood leukemia, but researchers continue to study these exposures.