Acute lymphoblastic leukaemia risks and causes

Acute lymphoblastic leukaemia is very rare in adults. About 8,300 people are diagnosed with leukaemia each year in the UK. Of these, only about 700 people have acute lymphoblastic leukaemia. About half the cases are in adults and half in children. ALL is the most common type of leukaemia in children.

ALL is more common in males than females. Some American research says that black people have a lower risk of developing ALL than white people

A risk factor is anything that can increase your chance of developing cancer - including leukaemia. Different cancers have different risk factors.

We don’t know what causes most cases of leukaemia. But the risk factors below may increase your risk of developing ALL

• Radiation exposure
• Exposure to benzene
• Smoking and alcohol
• Genetic conditions
• Past chemotherapy
• Viruses
• Electromagnetic fields
• Being overweight
• Paint exposure
• Weakened immunity

Other factors may lower leukaemia risk, such as being breastfed, allergies, and infections in childhood.

Remember that having a risk factor does not mean you will definitely get leukaemia. It is a rare disease. Many people with risk factors never get it. And some people with none of the risk factors do develop it. Risk factors are only a guide to what may increase your risk.

Radiation exposure

We’ve known for a long time that exposure to very high levels of radiation increases acute leukaemia risk. For example, people exposed to the atomic bomb explosions in Japan at the end of World War 2 had higher rates of leukaemia.

Some people worry that childhood X-rays cause leukaemia in children. A large study found there is very little evidence of any increase in risk, except in a type of leukaemia that is rare in children, called pre B cell ALL (or pre B ALL). But the researchers say that even this could be a chance finding and not a real risk increase.

There is some evidence that X-rays during pregnancy can increase risk of childhood leukaemia. So doctors avoid X-rays for pregnant women whenever possible.

Radon is a naturally occuring radioactive gas which can build up in houses in some areas of the UK. A Danish study has shown a higher risk of ALL in children living in houses with the highest levels of radon.

Exposure to benzene

Exposure to a chemical called benzene at work, over a long time, slightly increases risk of developing ALL. There is benzene in traffic pollution but the levels are likely to be too low to increase leukaemia risk. Benzene is also in cigarette smoke (see below).

Smoking and alcohol

A review of studies (meta-analysis) in 2009 has shown that smoking in the home by parents may increase the risk of ALL in their children. This includes smoking by the father in the time before conception. Two studies have shown a possible increased risk of leukaemia for children whose mothers drank alcohol during pregnancy. More research is needed into this issue.

Genetic conditions

Certain rare, inherited conditions can increase the risk of acute leukaemia, including

• Down’s syndrome
• Fanconi anaemia
• Ataxia telangiectasia

Past chemotherapy

People who have treatment with particular chemotherapy drugs (etoposide, mitoxantrone, amsacrine and idarubicin) have a slightly increased risk of developing ALL many years later. The risk depends on how much treatment you had. It is important to remember that this risk is still very small compared to the risk to your health if the cancer had not been treated.

Viruses

We know that a virus called HTLV-1 (human T cell leukaemia virus) increases the risk of developing a rare type of adult T cell leukaemia.

Electromagnetic fields

You may read in the press from time to time that some people are concerned about power lines and risk of cancer. Power lines produce high levels of 'low frequency electromagnetic radiation' (EMR).

Although some studies seem to suggest that exposure to very high levels of EMR could increase childhood leukaemia risk, the findings are not very clear. We don’t really know if the childhood leukaemia in these studies was actually caused by low frequency EMR. It could be due to some other common factors, or even chance. Scientists agree that we need more research before we can say for sure one way or the other. Fewer than 1 in 25 UK children are exposed to these high levels. Even if EMR is linked to childhood leukaemia, in the UK, only 1 in 100 cases (at most) are likely to be caused by it.

There is more information about electromagnetic radiation in the questions and answers section.

Being overweight

Some studies show that very overweight people (with a BMI of 30 or above) have a slightly higher risk of leukaemia than people with a normal bodyweight.

Paint exposure

One study has shown a higher risk of childhood ALL after exposure to paints, but more studies are needed to back up this finding.

Weakened immunity

An overview study (combined analysis) looked at published research into people with HIV or AIDS, or people treated with immunosuppressive medicines after an organ transplant. The researchers found that these people have a risk of leukaemia that is double or triple that of people without these conditions.

Breastfeeding

Researchers have pulled together the results of 17 separate studies. This showed that breastfed children have a very small reduction in ALL risk, compared to children who had not been breastfed.

Allergies

Some studies have shown a reduced risk of childhood ALL in people who have had allergies, including eczema, hay fever, asthma, or food or drug allergies.

Exposure to infection and childhood leukaemia

Studies show that children who go to nurseries or childminders from a young age have a lower risk of acute lymphoblastic leukaemia. The lower risk in these children may be due to exposure to infections. Children may have a slightly increased risk of ALL if they do not come across common infections from birth, but are exposed to them later in life.

A few studies have shown an increased risk for children of mothers who tested positive for Helicobacter pylori or Epstein Barr virus during pregnancy. These are both common infections and we need more research before we can be clear whether or not this is a risk factor for childhood leukaemia.