What is chronic lymphocytic leukaemia?

Chronic lymphocytic leukaemia (also called CLL or CLL leukemia) is the most common type of leukaemia. About 3,700 people in the UK are diagnosed with CLL each year. It is more common in older people.

We have separate information about other types of leukaemia.

How does chronic lymphocytic leukaemia develop?

Blood cells are made in the bone marrow. This is a spongy material found inside our bones. Every blood cell grows from a stem cell in the bone marrow. Normally, the stem cells make an early stage of the blood cell called a blast. These blasts develop into healthy blood cells.

There are two types of blood stem cell:

  • lymphoid stem cells – make a type of white blood cell called lymphocytes
  • myeloid stem cells – make red blood cells, platelets and all other types of white blood cell.

How blood cells divide

CLL is a cancer of the white blood cells, which develop from the lymphoid stem cells. In people with CLL, the bone marrow makes too many abnormal white blood cells called lymphocytes. These cells look normal under a microscope. But they are not fully developed (immature) and do not work properly.

Over time, these abnormal lymphocytes build up in the lymphatic system and may cause large, swollen lymph nodes. The abnormal lymphocytes can also build up in the bone marrow. This leaves less space for normal white blood cells, red blood cells and platelets to develop.

CLL usually develops very slowly, which is why it is called a chronic leukaemia. Acute leukaemias develop more quickly.

What are lymphocytes?

Lymphocytes are a type of white blood cell. They move around the body in the blood and the lymphatic system. Lymphocytes are an important part of the body’s defence. They fight against germs such as bacteria, fungal infections and viruses. They do this by:

  • killing germs directly
  • making special proteins called antibodies that stick to germs and make it easier for other white blood cells to find and kill them remembering and recognising germs – lymphocytes can live for a very long time, so they can quickly fight any infection you have had before.

Symptoms of chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia develops slowly and many people have no symptoms in the early stages. It is often discovered by chance after a routine blood test.

We have more information about the symptoms of leukaemia.

Causes of chronic lymphocytic leukaemia

It is not clear why people get chronic lymphocytic leukaemia. There are some things called risk factors that might increase the risk of developing it.

We have more information about risk factors and causes of CLL.

Diagnosis of chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia is often diagnosed after a routine blood test, and you may have had no symptoms at all.

If you do have symptoms, your GP will examine you and take a blood test to check the numbers of the different types of blood cell (called a full blood count). If they think you have CLL, they will refer you to a doctor who specialises in diagnosing and treating blood problems (haematologist). The haematologist will arrange further tests for you.

At the hospital

The haematologist will ask you about any illnesses or health problems you have had. They will check whether your lymph nodes, spleen or liver are enlarged. They will also do more detailed blood tests to check whether you have CLL cells in your blood.

To help you understand some of the tests used to diagnose CLL, it can be helpful to know a bit more about the cells.

In many people with CLL, the leukaemia cells are mainly in the bloodstream and the bone marrow. If the leukaemia cells are mainly in the lymph nodes, the disease is called small lymphocytic lymphoma (SLL). CLL and SLL are now considered to be the same disease.

We have more information about how CLL is diagnosed.

Chronic lymphocytic leukaemia stages

Doctors use staging to find out how much leukaemia there is in the body. This helps them know when you may need treatment and which treatment is best for your situation.

We have more information about staging of CLL.

Treatment for chronic lymphocytic leukaemia

A team of specialists will meet to discuss the best possible treatment for you. This is called a multidisciplinary team (MDT).

Your cancer doctor or specialist nurse will explain the different treatments and their side effects. They will also talk to you about certain things to think about when making treatment decisions.

Only a small number of people with CLL need to start treatment straight away. Doctors usually wait until there are signs the CLL is progressing before suggesting you have treatment. This is called monitoring (watch and wait).

Most people who do need treatment are treated with a combination of 2 types of treatment. These are:

Other treatments that are sometimes used include the following:

  • Supportive therapy

    You may have supportive therapy to help control any symptoms caused by CLL, such as infections or anaemia.

  • Donor stem cell transplant

    Doctors may suggest a donor cell transplant if the CLL has not responded to other treatments or if it is a type of CLL that is unlikely to respond.

  • Radiotherapy

    Radiotherapy is only used in certain situations. For example, you may have it if you have enlarged lymph nodes or an enlarged spleen.

  • Surgery

    This is occasionally used to remove an enlarged spleen (splenectomy).

You may have some treatments as part of a clinical trial.

We have more information about treatment for CLL.

Living with chronic lymphocytic leukaemia

Follow-up and monitoring

Chronic lymphocytic leukaemia often progresses very slowly. This means that people who have CLL can live with it for a long time. If you do need treatment, it is usually very effective and can keep the leukaemia under control for many years. You will need to have regular check-ups and blood tests.

If you have any problems or notice any new symptoms, let your doctor know as soon as possible. Do not wait until your next appointment.


You may want to make changes to your lifestyle. Even if you had a healthy lifestyle before your diagnosis, you may want to focus more on making the most of your health.

A healthy lifestyle does not have to be difficult or expensive. It is about making small changes to the way you live. This will improve your health and sense of well-being. It will also lower your risk of getting other illnesses and some other cancers.

When planning changes, you need to take any side effects of treatment into account. Try not to do too much, too soon.

Understanding more about CLL and its treatment can help you cope. It means you can discuss treatment, tests and check-ups with your doctors and nurses, and be involved in making decisions. This can make you feel more confident and give you back a feeling of control. Here are some things to consider:

  • Get involved in your healthcare

    This includes taking your medicines as prescribed and always going to your hospital appointments. If you have any problems or notice any new symptoms between your appointments, let your doctor know as soon as possible.

  • Self-help and support groups

    Talking about your feelings can help reduce stress, anxiety and isolation. Self-help or support groups offer a chance to talk to other people who may be in a similar situation and facing the same challenges as you.

  • Online support

    There are online support groups, social networking sites, forums, chat rooms and blogs for people affected by leukaemia. You can use these to ask questions and share your experience. You can find details of our Online Community below.

Getting support

Everyone has their own way of dealing with illness and the different emotions they experience. You may find it helpful to talk things over with family and friends or your doctor or nurse. 

The organisations below offer information and support:

  • Anthony Nolan
    Anthony Nolan is the UK’s largest stem cell and bone marrow register.
  • Blood Cancer UK
    Blood Cancer UK is a blood cancer research charity that provides information and support on any type of blood cancer.

Macmillan is also here to support you. If you would like to talk, you can:

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Helen Marr, Consultant Haematologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Reviewed: 30 June 2018
Reviewed: 30/06/2018
Next review: 31 January 2020
Next review: 31/01/2020

This content is currently being reviewed. New information will be coming soon.