What is chronic lymphocytic leukaemia (CLL)?

Chronic lymphocytic leukaemia (also called CLL or CLL leukemia) is the most common type of leukaemia. About 3,800 people in the UK are diagnosed with CLL each year. It is more common in older people.

We have separate information on other types of leukaemia.

How does CLL develop?

Blood cells are made in the bone marrow. The bone marrow is a spongy material in the middle of our bones. All blood cells are made from blood stem cells. These are blood cells at the earliest stage of their development. The new, developing blood cells are called blast cells.

There are 2 types of blood stem cell:

  • lymphoid stem cells make a type of white blood cell called lymphocytes.
  • myeloid stem cells make all the other types of blood cell. These include red blood cells, platelets, and other types of white blood cells, such as neutrophils.
How blood cells divide
Image: How blood cells divide

CLL is a cancer of the white blood cells, which develop from B lymphocytes. 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. Many people with CLL do not need treatment for months or years. If you have symptoms, you may need treatment sooner.

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

Small lymphocytic lymphoma

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 and are treated in the same way.

Symptoms of chronic lymphocytic leukaemia (CLL)

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 and risk factors of chronic lymphocytic leukaemia (CLL)

We do not know what causes CLL, but research is going on to find out more about it. Certain things called risk factors can increase the risk of developing it. These are:

  • Age

    The risk of developing CLL increases with age. Most people diagnosed with CLL are aged over 60. It is rare in people under 40.

  • Sex

    CLL is more common in men than women.

  • Family history

    Most people with CLL have no family history of it. But studies show that there is an increased risk of developing CLL if you have a close relative who has it. A close relative is a parent, sibling, or child. If anyone else in your family has CLL, it is important to tell your specialist.

    Most people who have a relative with CLL will never develop it themselves.

    CLL is not infectious and cannot be passed on to other people.

  • Ethnicity

    CLL is most common in people of European origin.

Diagnosing chronic lymphocytic leukaemia (CLL)

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

The blood tests you may have include:

  • Immunophenotyping

    Immunophenotyping checks for CLL cells in the blood.

  • Cytogenetic testing

    Cytogenetic testing looks at all the chromosomes in the leukaemia cells.

  • Fluorescent in situ hybridisation (FISH) testing

    Fluorescent in situ hybridisation (FISH) testing is an important cytogenetic test used to look for a small number of specific changes in genes or chromosomes in the CLL cells.

  • Immunoglobulin testing

    Immunoglobulin testing checks the levels of antibodies you have in your blood for fighting infection.

  • Direct Coombs test

    Direct Coombs test checks if the CLL cells are making antibodies that can damage your red blood cells.

You may also have further tests, such as:

  • Chest x-ray

    A chest x-ray takes a picture of your chest, to check your lungs and heart. The x-ray also looks at lymph nodes in your chest.

  • CT scan

    A CT scan takes a series of x-rays, which build up a 3D picture of the inside of the body. A CT scan is sometimes used to check how many lymph nodes are affected by CLL. It can also be used to see whether the spleen is enlarged.

  • Bone marrow biopsy

    You may have a bone marrow biopsy. This is used to check how much CLL is in the bone marrow.

  • Lymph node biopsy

    You will not usually need a lymph node biopsy. But some people with CLL may have one. People with small lymphocytic leukaemia may also need a lymph node biopsy. Your cancer doctor or specialist nurse can explain whether this is right for your situation.

    An enlarged lymph node or a small section of lymph node is removed so it can be looked at under a microscope. You may have this done under a local or general anaesthetic. It is a small operation and most people can go home on the same day. After the operation, you have a small wound with a few stitches. The stitches are usually taken out after 7 to 10 days.

Stages of chronic lymphocytic leukaemia (CLL)

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 (CLL)

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 treatment options 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:

  • targeted therapy – are a kind of drug therapy used to find and attack leukaemia cells.
  • chemotherapy – chemotherapy uses anti-cancer (cytotoxic) drugs to destroy or damage leukaemia cells.

Other treatments that are sometimes used include:

  • 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).

We have more information about treatment for CLL.

Living with chronic lymphocytic leukaemia (CLL)

Follow-up and monitoring CLL

CLL often progresses very slowly. This means that people with 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. You may attend the hospital for these, or they may be done by your GP.

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


You may want to find out more about having a healthier lifestyle. This will help you stay as well as possible. Some examples of having a healthy lifestyle include:

  • having a well-balanced diet
  • being physically active
  • reducing stress
  • being involved in your healthcare.

There are many benefits of having a healthy lifestyle. It does not have to be difficult or expensive. You could try going for a daily walk or doing some exercises at home. This will improve your health and well-being, and lower your risk of getting other illnesses and some cancers.

When planning changes, you need to consider how the side effects of treatment might affect you. Try not to do too much, too soon.

Understanding more about CLL and its treatment can also help you cope. It can help you talk to your doctors and nurses about your treatment, tests and check-ups. It can also help you be involved in making decisions. This can make you feel more confident and give you back a feeling of control.

  • 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 appointments that do not go away within a couple of weeks, tell your doctor 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. 

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:

  • Call the Macmillan Support Line on 0808 808 00 00.
  • Chat to our specialists online.
  • Visit our CLL, SLL, HCL forum to talk with people who have been affected by chronic lymphocytic leukaemia (CLL), share your experience, and ask an expert your questions.

About our information

  • References

    Below is a sample of the sources used in our chronic lymphocytic leukaemia (CLL) information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    Schuh A et al. Guideline for the treatment of chronic lymphocytic leukaemia. British Society for Haematology Guidelines. July 2018.

    Eichhorst B et al. Chronic lymphocytic leukaemia: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. ESMO Guidelines Committee. October 2020.

  • 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 Anne Parker, 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.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 February 2022
Next review: 01 February 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.