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What is chronic lymphocytic leukaemia (CLL)?

We're here for you if you want to talk

0808 2080 888

[email protected]

CLL is the most common type of leukaemia in adults in the UK with around one in 200 people developing CLL at some point in their life.

CLL is a chronic condition, which means it usually develops very slowly.

If you have CLL, your body produces too many lymphocytes (a type of white blood cell) that don’t work properly. These cells won’t fight infection as well as normal white blood cells do, and they multiply in an uncontrolled way and stop normal blood cells from working properly. This is what causes most of the symptoms that people get when they have CLL.

CLL and your immune system

Your immune system is a network of cells, tissues and organs which protect your body against infection. It’s able to react quickly to infections it’s seen before, and lymphocytes play an important role in this. They circulate around your body in your blood and fight infections.

CLL affects B lymphocytes, which normally produce antibodies to fight infections. Because of this, it often affects your body’s defences. This means you might get:

  • infections that are more severe than usual and last longer
  • auto-immune conditions, because your immune system can get confused and damage some of your tissues
  • shingles, an infection of the nerve and the skin around it.

CLL and your lymphatic system

A network of thin tubes called lymph vessels runs around your body. This is your lymphatic system. The vessels collect fluid called lymph and return it to your blood.

Along the lymph vessels are small lumps of tissue called lymph nodes or lymph glands. There are many of these in your body. If you get an infection when you’re healthy, these can swell and become tender – people usually call them 'swollen glands'.

Although CLL mainly affects the bone marrow, it often causes swelling in lymph nodes because abnormal lymphocytes build up in them. The ones in your neck, armpits and groin are often affected but, more rarely, those in your gut lining can be too. CLL can also cause swelling in your spleen, the most important organ in your immune system, meaning that it can’t work properly.

We have general information about blood cancer and the immune and lymphatic systems.

Small lymphocytic leukaemia (SLL)

If CLL is affecting your lymphoid tissues a lot, it may be called small lymphocytic lymphoma (SLL), which is a type of CLL. Your treatment will still be the same though and your condition won’t develop any differently.

Causes of CLL

When you’re diagnosed with any cancer, one of the first things you might think is: why me?

With CLL, there are no clear reasons. Here’s what we do know:

  • CLL is the most common type of leukaemia in adults.
  • Of all people diagnosed with leukaemia, around a third are diagnosed with CLL.
  • About one person in 200 will develop CLL at some point in their life.

Possible risk factors

People who get CLL are usually in their 70s or older. It’s very rare for people under 40 to get CLL, but about 10% of patients are under 55 when diagnosed. Children don’t get CLL.

Men are about twice as likely as women to get it – we don’t know why.

A parent, child, brother or sister of someone with CLL has a slightly higher chance than others of developing the condition, but the risk for any individual is still very low.

Because of this, experts don’t recommend testing family members unless they’re being considered as donors for a stem cell transplant – which is rare for people with CLL.

CLL is more common in white people – we don’t know why.

There’s a condition called monoclonal B-cell lymphocytosis (MBL) where people have very low levels of CLL-like cells in their blood, but no symptoms.

Not all people with MBL go on to get CLL. However, we think that most people diagnosed with CLL previously had MBL, possibly for many years.

Experts don’t recommend testing family members for MBL unless they’re being considered as donors for a stem cell transplant.

There have been some suggestions that exposure to radiation or certain chemicals may increase your risk of developing CLL, but this link hasn’t been proven.