Chronic myeloid leukaemia (CML) risks and causes

About 610 people are diagnosed with CML each year in the UK. So it is quite a rare condition. It is more common in men than women.

We don't know the cause of most cases of leukaemia but there are some factors that may increase your risk. Anything that increases your risk of getting a disease is called a risk factor. Different cancers have different risk factors. This page discusses the risk factors for CML. Even if you have one or more of the risk factors below, it does not mean that you will definitely get CML.

CML is slightly more common in men than women. As people get older their risk of CML increases but as CML is rare the risk is still small.

We mention the Philadelphia chromosome here because people have heard about it. But it isn't really a risk factor. You can't inherit it, or pass it on to your children. It is really a change in a gene that is associated with CML.

Most people with CML are found to have an abnormal chromosome, called the Philadelphia chromosome. It is caused by some of the DNA from one chromosome (no. 9) getting stuck onto another chromosome (no. 22). This is a called a translocation, a known type of genetic abnormality. The Philadelphia chromosome makes the cell produce a protein that encourages the leukaemic cells to grow and multiply. It is this chromosome change that causes CML.

We know that radiation can increase risk to some extent because atomic bomb survivors had an increased risk of leukaemia. A 20 year study has followed up workers who helped clean up after the Chernobyl nuclear power plant accident in 1986. It shows that even at low doses of radiation there is an increased risk of all types of leukaemia. 

If you have had radiotherapy for another cancer in the past, this could increase your risk of developing CML. But this risk is very small, compared to the benefit of the radiotherapy in treating the cancer.

An analysis of published studies has shown that people with low immunity due to HIV or AIDS are 3 times more likely to develop leukaemia than the general population. People who take drugs that lower their immunity after an organ transplant are twice as likely to develop leukaemia.

Various studies have shown that people with inflammatory bowel conditions, such as ulcerative colitis or Crohn's disease, have a higher risk of chronic myeloid leukaemia compared to the general population.

A review looked at published evidence for men exposed to pesticides as part of their work (for example, farmers or agricultural workers). The review showed that the men had a 40% increase in their CML risk compared to the general population.

Contact with a chemical called benzene for some years may increase CML risk. Benzene is one of the chemicals in petrol. It is also a solvent used in the rubber industry. But most people in the UK wouldn't come into contact with enough benzene for it to increase their risk at all.

A combined review of 4 previously published studies showed that the risk of CML is increased by about a quarter for people who are overweight or obese, compared to people with a healthy bodyweight.

Electromagnetic fields are often talked about as a possible risk factor but they probably do not increase the risk of chronic myeloid leukaemia. We are all exposed to electromagnetic radiation. It is all around us. Some research has suggested this might be a risk factor for leukaemia. But no increase in the risk of CML has ever been found in adults exposed to the normal background levels of electromagnetic fields in their own homes.