Chronic myeloid leukaemia (CML) risks and causes

Around 8,300 cases of leukaemia are diagnosed each year in the UK. Around 3,800 of these are chronic leukaemias, but only about 630 of these are CML. So it is quite a rare condition.

We don't know the cause of most cases of leukaemia but there are some factors that may increase your risk. A risk factor is something that may make you more likely to develop a particular condition or disease. For example, smoking is a risk factor for lung cancer and sun exposure is a risk factor for skin cancer.

CML is most common in older age. It 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 radiation can increase risk to some extent because atomic bomb survivors had an increased risk 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.

One study showed that people with the inflammatory bowel condition, ulcerative colitis, have almost double the risk of 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.