Chronic lymphocytic leukaemia (CLL) risks and causes

In total, counting all types, there are around 8,300 cases of leukaemia diagnosed in the UK each year. About 3,100 of these are chronic lymphocytic leukaemia.  CLL is the most common type of chronic leukaemia by far.

It is much more common to get CLL if you are older. It is more common in people over 60 and is very rare under 40. Men are twice as likely to develop CLL as women. We don't know why that is.

Although leukaemia is the most common type of childhood cancer, leukaemia in children is nearly always acute leukaemia - either acute myeloid leukaemia or acute lymphoblastic leukaemia. Chronic leukaemia is very rare in children.

We don't know the cause of most cases of leukaemia but there are some risk factors that may increase your risk of developing chronic leukaemia. A risk factor is something that may make you more likely to develop a particular condition or disease.

We know that there is some kind of inherited genetic change in some people who develop CLL. It is much less common in some ethnic groups, for example. We know that CLL can run in families. But so far, we don't know of any specific gene changes that are linked to CLL. Studies show that people with a first degree relative with CLL have a 6 to 9 times increased risk of developing it themselves.

One study has shown that first degree relatives of people diagnosed with Hodgkin’s lymphoma have double the risk of CLL. Although there is some evidence of CLL running in families, it is important to remember that most cases of CLL do not have a family link.

One study has shown a doubled risk of CLL in people with a first degree relative diagnosed with a blood disorder called monoclonal gammopathy of undetermined significance. Having a first degree relative with lymphoplasmacytic lymphoma or Waldenström's macroglobulinemia has been shown in one study to triple the risk of CLL.

Results of a large European study showed that men with diabetes had double the risk of B cell chronic lymphocytic leukaemia. But women with diabetes did not have an increased risk. We need more research to find out why this is.

Some studies have shown that people who have had certain medical conditions have a slightly increased risk of developing CLL. The conditions include the following. 

• Pneumonia (chest infection)
• Sinusitis
• Herpes zoster infection
• Autoimmune haemolytic anaemia
• Chronic osteoarthritis
• Inflamed prostate (prostatitis)

It is possible that some of these conditions are due to reduced immunity in the early stages of CLL, rather than the cause.

Electromagnetic fields are often talked about as a possible risk factor for developing leukaemia. We are all exposed to electromagnetic radiation. It is all around us. Some research has suggested that electromagnetic fields might be a risk factor for leukaemia. But no increase in the risk of CLL has ever been found in adults who are exposed to the normal background levels people generally have in their own homes.

An overview of published evidence has shown that people with low immunity due to HIV or AIDS are 3 times more likely than the general population to develop leukaemia. People treated with medicines to lower their immunity after an organ transplant have a risk that is double that of the general population.

Two studies have shown an increased risk of CLL in women who have used hair dye. In one of these studies, only women who had used permanent black hair dye had an increased risk, while the other study an increase in risk only for women who used hair dyes before 1980. More studies are needed to clarify if hair dye use today increases risk of CLL.

One study that combined the results of 4 previous studies showed that people who are very overweight (obese) have a slightly increased risk of CLL. We need more research to be sure that being overweight really increases the risk of CLL.

Radiation is known to increase the risk of other types of leukaemia but has not generally been linked to an increased risk of CLL. But one study has showed an increased risk of CLL in Czech uranium miners who had high exposure to radon (a radioactive gas).