Leukemia is due to a series of mutations in genes that control the growth of cells, which leads to their uncontrolled growth in the bone marrow. While the exact causes of this are unknown, several risk factors for the disease have been identified. Known risk factors vary with the different types of leukemia but include radiation (from atomic bomb exposures to medical radiation), exposures to chemicals such as benzene and pesticides, previous chemotherapy, some infections, and certain genetic conditions. There are others still under investigation as well, such as radon.
Chronic leukemia is much more common in older adults, and though acute leukemia is often thought of as being a childhood cancer, acute myeloid leukemia is actually much more common in adults. For unknown reasons, men are more likely than women to develop the four major types of leukemia.
Confirmed and Probable Risk Factors
There are several risk factors for the development of leukemia that have been documented in a number of studies. A risk factor is something that is associated with an increased risk of developing leukemia but does not necessarily cause the disease. Some of these include:
Age as a risk factor for leukemia varies widely with the type of leukemia. Together, acute lymphocytic leukemia (ALL) and acute myelogenous leukemia (AML) account for 30 percent of childhood cancers.
While many people consider these diseases pediatric cancers, AML is actually much more common in adults (the average age at diagnosis is 68). Around 40 percent of cases of ALL are in adults; when diagnosed in childhood, it is most common in children under the age of 5 years.
Chronic lymphocytic leukemia (CLL) and chronic myelogenous leukemia (CML) are much more common in older adults and are very uncommon in people under the age of 40.
The primary types of leukemia (AML, ALL, CML, and CLL) are slightly more common in males than females, but the reason for this is unknown.
Children who have high birth weights (weight at birth greater than 8.9 pounds or 4000 grams) have a greater risk of developing ALL.
Racial differences in incidence differ between the types of leukemia.
ALL has the highest incidence in Hispanic whites, followed by non-Hispanic whites and Asian and Pacific Islanders, with the lowest incidence in blacks.
CLL is more common in non-Hispanic whites, followed by blacks, with the lowest incidence in Hispanics and Asian and Pacific Islanders.
AML is similar among people of different ethnic backgrounds during childhood, but in adults is more common in non-Hispanic whites.
CML is most common in non-Hispanic whites followed by blacks and then Hispanics, with the lowest incidence in Asian and Pacific Islanders.
Some types of radiation are known risk factors for leukemia, and others are only possible risk factors. There are two primary types of radiation:
- Non-ionizing radiation: This type of radiation is fairly weak and includes the type that is emitted from a cell phone or computer terminal. While some concerns have been raised, such as the concern about brain tumor risk and cell phones, the risk is considered relatively small.
- Ionizing radiation: In contrast, ionizing radiation has been linked to leukemia. This type of radiation has much more energy—enough to break certain chemical bonds, remove electrons from atoms, and damage DNA in cells.
There are a number of different ways in which ionizing radiation has been associated with leukemia. These include:
- Atomic bomb radiation: Survivors of the Hiroshima and Nagasaki atomic bombings had a significantly increased risk of developing leukemia.
- Nuclear accidents: Survivors of the 1986 Chernobyl nuclear reactor disaster had an increased risk of leukemia two to five years after the meltdown. Those who were highly exposed had twice the risk of developing leukemia as those not exposed.
- Medical diagnostic radiation: Ionizing radiation was found to be carcinogenic (or cancer-causing) only a few years after X-rays were discovered, and concern has been raised in recent years over the danger of too much medical radiation, particularly in children. The risk varies, with imaging tests such as CT scans, bone scans, and PET scans involving much more radiation than plain X-rays. (MRI scans use magnets and do not involve exposure to radiation.)
- Medical therapeutic radiation: Radiation therapy for cancer can increase the risk of developing leukemia (especially AML), with the risk highest in the period five to nine years after radiation. The risk varies with the site of radiation as well as the dose used.
- Radioactive iodine therapy: Receiving radioactive iodine therapy as a treatment for hyperthyroidism or thyroid cancer is associated with an increased risk of leukemia, with the risk of AML being 80 percent higher than for those who didn’t receive this therapy. The risk is even higher for CML, with those exposed having a risk 3.5 times higher than average.
- Air and space travel: Air flight, especially over the far north, involves exposure to cosmic radiation, but this amount of ionizing radiation is relatively small. The leukemia risk from space travel due to galactic cosmic rays, however, is a subject of great interest among those looking at travel to places such as Mars in the future.
- Radioactive materials: Uranium mining as an occupation increases the risk of leukemia. There has also been concern about exposure to radioactive material in tobacco products, which pick up these materials in the soil where they are grown.
While the benefits of chemotherapy usually far outweigh the risks, some chemotherapy drugs can predispose a person to leukemia later on. This is true even for the drugs commonly used for early-stage breast cancer. For most of these drugs, the risk begins to increase two years after treatment and peaks between five and 10 years after treatment.
AML is the form of leukemia most often associated with chemotherapy, but ALL has also been linked to the treatment. Examples of drugs associated with leukemia include Cytoxan (cyclophosphamide); Leukeran (chlorambucil); VePesid (etoposide); Vumon (teniposide); Gleostine, CeeNu, and CCNSB (lomustine); Gliadel and BiCNU (carmustine); Myleran (busulfan); Mustargen (mechlorethamine); and Novantrone (mitoxantrone).
Drugs such as Adriamycin (doxorubicin) and other anthracyclines, Platinol (cisplatin) and other platinum drugs, and bleomycin have been associated with leukemia but less commonly than the drugs mentioned earlier.
Some medical conditions are associated with an elevated risk of developing leukemia. Myelodysplastic syndromes are disorders of the bone marrow that have been referred to as “preleukemia” and carry a significant risk of developing into AML (up to 30 percent). Other conditions such as essential thrombocytopenia, primary myelofibrosis, and polycythemia vera also carry an increased risk.
Furthermore, people who are immunosuppressed, such as those who take immunosuppressive medications due to an organ transplant, have a significantly increased risk of developing leukemia.
Associations have been noted between leukemia in adults and medical conditions such as inflammatory bowel disease (ulcerative colitis and Crohn’s disease), rheumatoid arthritis, systemic lupus erythematosus (lupus), celiac disease, and pernicious anemia, among others. However, a large 2012 study looking into these associations only found an increased risk relationship with ulcerative colitis and AML, and peptic ulcer disease and CML.
Genetic syndromes may also increase the risk of leukemia (see below).
Adding to the list of cancers caused by smoking, tobacco use is associated with a significantly increased risk of AML. At the current time, it’s thought that around 20 percent of AML cases are linked to smoking. There is some evidence that leukemia in children may be linked with parent’s smoking, and mothers exposed to secondhand smoke appear to have a slightly elevated risk of developing ALL.
Home and Occupational Exposures
There are a number of exposures that have been associated with leukemia, though the risk varies with the different types of the disease. Some of the substances have been linked clearly in many studies, while others are still uncertain. Some exposures of interest include:
- Benzene: Benzene is a known carcinogen that is present in a number of materials, such as some paints, solvents, plastics, pesticides, detergents, and unleaded gasoline. Benzene is also a byproduct of the combustion of coal. Benzene in tobacco smoke is thought to be one of the reasons why smoking is strongly linked to AML. Maternal and childhood exposure to paint at home is associated with an elevated risk of ALL. Home use of petroleum solvents is associated with an increased risk of childhood AML.
- Home pesticide exposures: Pesticide exposure during pregnancy and childhood appears to be associated with an increased risk of leukemia, according to several studies.
- Contaminated drinking water: An increased risk of leukemia was found among those at a U.S. Marine Corp base camp in North Carolina that was contaminated by a solvent between 1950 and 1985.
- Formaldehyde: Medical workers and embalmers have an increased risk of myeloid leukemias. While exposure is common in these workers, but many people are exposed to formaldehyde through the “off-gassing” of formaldehyde from pressed wood products (such as particleboard, plywood, and fiberboard). Formaldehyde exposure such as this is considered to be a known carcinogen, but it’s not clear what level of exposure (amount or duration) might be a problem. Other sources of formaldehyde include some glues and adhesives, some insulation materials, and some paper product coatings. Like benzene, formaldehyde is also found in tobacco smoke.
Noting that the incidence of childhood leukemia has been increasing in California, studies looking at environmental exposures that may be associated with this risk are in progress.
Infection with the human T-cell leukemia virus (HTLV-1) increases the risk of leukemia. The virus is a retrovirus (similar to HIV) and infects the type of white blood cells known as T lymphocytes or T cells. HTLV-1 is spread in a way similar to HIV; it can be transmitted through blood transfusions, through sexual contact, by sharing needles among IV drug abusers, and from a mother to a child during delivery or through breastfeeding.
HTLV-1 is relatively uncommon in the United States, but is found in the Caribbean (especially Haiti and Jamaica), Japan, central and west Africa, and Middle East (especially Iran). It’s thought that between 1 percent and 4 percent of people who are exposed to the virus will develop leukemia; the most common age of onset is between 30 and 50.
While alcohol consumption is linked with a number of cancers, a 2014 study found no association between alcohol use and the four major types of leukemia. There has been a link noted, however, between maternal alcohol consumption during pregnancy and AML in children born to these mothers.
Possible Risk Factors
In addition to known and probable risk factors for leukemia, there are several risk factors that are being evaluated for their association with leukemia. Some possible risk factors include:
With many types of leukemia, especially acute leukemia in children, there appears to be little association with dietary practices. In CLL, however, the most common type of leukemia in American adults, diet may play a role. A 2018 study in Spain found that those who ate a Western diet were 63 percent more likely to develop CLL than those who consumed a Prudent diet or Mediterranean diet.
There has been controversy surrounding a possible connection between the artificial sweetener sucralose and cancer.
Sucralose (with brand names including Splenda and others) was approved in 1999 and is currently in thousands of products worldwide. Despite a multitude of reassuring studies prior to its approval, a 2016 Italian study on mice found that rodents who were exposed to sucralose throughout their lives (beginning in utero) had a significantly increased risk of developing leukemia. It’s important to note that this was an animal study, and the doses given were equivalent to an adult consuming four times the average amount of sucralose every single day. That said, with the popularity of sucralose as a sugar substitute, it’s thought that young children could easily exceed the FDA’s acceptable daily intake of 5 mg/kg daily.
(Keep in mind that, despite a focused concern about sucralose, questions have been raised about the use of other artificial sweeteners as well. Ideally, any of these products should be used sparingly in a healthy diet.)
Electromagnetic Fields (Power Lines)
Since 1979, when a study found an increased risk of leukemia in children who lived near high voltage power lines, a number of studies have looked at this possible association with mixed results. Some showed an increased risk with high levels of exposure, and others showed little, if any, effect. Three analyses that have compared results of studies to date (totaling 31 studies in all) found that high exposures (0.3 uT or higher) were associated with a 1.4 to 2.0 times increased risk of leukemia. This level of exposure, however, is not common. In these studies, only 0.5 percent to 3.0 percent of children had an exposure equal to or exceeding 0.3 uT.
At the current time, there is a possibility that radon in homes, a form of ionizing radiation, may increase the risk of chronic lymphocytic leukemia (CLL). Radon is a well-known carcinogen, and it’s thought that roughly 27,000 people die from radon-induced lung cancer each year in the United States.
Radon is an odorless, colorless gas, that is produced by the normal breakdown of uranium found in the soil and rocks beneath homes. Elevated levels have been found in all 50 states, and the only way to know if you are at risk is to do radon testing.
A 2016 study found that the areas in the United States where CLL is most common are also the regions known to have the highest radon levels (northern and central states). While the association between radon and leukemia is uncertain, some researchers propose that radon could lead to leukemia in a way similar to how it increases lung cancer risk.
Coffee and Tea
Coffee and tea have both been looked at with regard to the risk of leukemia, and the studies have been mixed. Some indicated an increased risk with more consumption, while others instead showed a potential protective effect (a reduced risk of leukemia). Since people metabolize coffee and tea in different ways (fast metabolizers vs. slow metabolizers), it could be that the effects vary between different people.
While some studies have found no association between level of physical activity and leukemia, a 2016 study found that people who engaged in more “leisure physical activity” were around 20 percent less likely to develop myeloid leukemias than those who were less active.
The role of family history and genetics varies between the different types of leukemia.
ALL does not appear to run in families, with the exception being identical twins, in which one of the siblings in the pair has an increased risk of developing ALL if the other developed the disease before one year of age. That said, there are certain genetic syndromes that are associated with an increased risk of this type of leukemia (see below).
In contrast, family history plays an important role in CLL. People who have a first-degree family member who has had CLL (parent, sibling, or child) have more than twice the risk of developing the disease themselves.
A family history of AML in first-degree relatives increases risk, but the age at diagnosis is important. Siblings of children with AML have up to a four times higher risk of developing the disease, with the risk in identical twins being around 20 percent. In contrast, children who have a parent who has adult-onset leukemia do not appear to be at a higher risk.
Family history doesn’t appear to play a significant role in the development of CML.
Genetic conditions and syndromes that are associated with an increased risk of some types of leukemia include:
- Down syndrome (trisomy 21): People with Down syndrome have roughly a 20 percent increased risk of developing leukemia (AML and ALL). The incidence is highest in children under the age of 5 years.
- Klinefelter’s syndrome (XXY)
- Fanconi anemia
- Li-Fraumeni syndrome
- Ataxia telangiectasia
- Bloom syndrome
- Wiskott Aldrich syndrome
- Schwachman-Diamond syndrome
- Blackfan-Diamond syndrome
- Kostmann syndrome