Chronic lymphocytic leukaemia (CLL)
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What is chronic lymphocytic leukaemia (CLL)?
Chronic lymphocytic leukaemia (CLL) and small lymphocytic lymphoma (SLL) are slow growing types of blood cancer. They develop when B cells become abnormal (cancerous) and build up in different parts of the body. B cells are white blood cells that normally help fight infection.
We have separate information about other types of leukaemia.
CLL and SLL are treated as different forms of the same blood cancer. The main difference is where the cancer cells are found:
- CLL is found in the blood, bone marrow or lymph nodes
- SLL is found in the lymph nodes but not in the blood or bone marrow.
In this information, we use the term CLL to refer to both types. We will explain any other important differences.
The blood, bone marrow and lymphatic system
To help understand CLL and its treatment, it is useful to know more about the blood, bone marrow and lymphatic system.
Blood cells are made in the bone marrow. This is a spongy material found inside our bones. Normally, the bone marrow makes millions of new blood cells every day to replace ones that are old and damaged. This keeps the numbers of each type of blood cell at the right level so the body can work properly.
The bone marrow
Every blood cell grows from a stem cell in the bone marrow.
There are 2 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.
The stem cell divides to make an early stage of the blood cell. This is called a blast cell. Blast cells are young and not fully developed. They cannot do the job of a normal cell. Usually, they stay in the bone marrow until they are fully developed.
How blood cells divide
When a cell is ready, it moves from the bone marrow into the blood to do different jobs:
- Red blood cells contain haemoglobin (Hb). Haemoglobin binds to oxygen. Red blood cells can then carry oxygen from the lungs to all the cells in your body.
- Platelets are very small cells that help blood to clot. They prevent bleeding and bruising.
- White blood cells help fight and prevent infection. There are several types of white blood cell. The most important types are called neutrophils and lymphocytes.
The lymphatic system is part of the body’s immune system. It protects us from infection and disease.
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Booklets and resources
Symptoms of CLL
CLL develops slowly and many people have no symptoms in the early stages. It is often discovered by chance after a routine blood test.
The symptoms of CLL can include the following:
- feeling very tired (fatigued)
- having frequent infections
- swollen lymph nodes in the neck, armpits or groin
- bruising and bleeding easily
- high temperatures (fever) or heavy drenching sweats
- unexplained weight loss
- a lack of appetite
- discomfort in the upper-left hand side of the tummy.
Signs and symptoms of CLL
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Causes of CLL
Around 4,700 people are diagnosed with CLL every year in the UK. We do not know the exact cause of CLL. But there are risk factors that can increase your chance of developing it. These are:
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Age
The risk of developing CLL increases with age. Most people diagnosed with CLL are aged over 70. It is rare in people under 40.
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Sex
CLL is more common in men people assigned male at birth than in women and people assigned female at birth.
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Family history
Most people with CLL have no family history of it. You cannot pass it on to your children. 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.
CLL is rare. 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.
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Monoclonal B-cell lymphocytosis (MBL)
Some people have a very low level of abnormal B cells in their blood without any other signs of having CLL. This is a pre-cancerous condition called monoclonal B-cell lymphocytosis (MBL).
Most people never know they have MBL. It is more common in people over 60. Each year, around 1 to 2 people out of every 100 people with MBL (1 to 2%) develop CLL. People with MBL have regular blood tests to check their level of abnormal cells.
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Ethnicity
CLL is most common in people of European origin.
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Diagnosing CLL
CLL is often diagnosed after a routine blood test. Many people have no symptoms when they are diagnosed.
If you do have symptoms, your GP will examine you and do a blood test. If they think your symptoms could be caused by CLL, they will refer you to a specialist doctor.
The blood tests you may have include:
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A blood film test
A blood film test checks what your blood cells look like under a microscope. It is used to check for abnormal cells and can be used to help with diagnosing CLL.
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Immunophenotyping
Immunophenotyping is a test that can be done on a blood or bone marrow sample. It looks for certain proteins on the surface of cancer cells. The results usually confirm a diagnosis of CLL.
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These are tests to help plan treatment. The most common genetic tests include:
- FISH (fluorescent in situ hybridisation) – these tests look for specific changes in the genes or chromosomes in CLL cells
- TP53 – this checks the TP53 gene that is usually found in a part of chromosome 17 (called 17p)
- IGHV – this test checks for the IGHV gene.
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Immunoglobulin testing
Immunoglobulin testing checks the level of antibodies in the blood for fighting infection.
Your specialist may arrange further tests to find out more about the cancer. You may have:
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CT scan
A CT scan creates a detailed picture of the inside of the body. The picture is built up using x-rays taken by a CT scanner.
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Bone marrow biopsy
You may have a bone marrow biopsy. This is to check how much CLL is in the bone marrow.
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Lymph node biopsy
Some people with CLL may have a lymph node biopsy. Your doctor or specialist nurse can explain whether this is right in 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.
Waiting for test results can be a difficult time. We have more information that can help.
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Staging of CLL
The results of your tests help your doctors find out more about the size and position of the cancer and whether it has spread. This is called staging.
Knowing the stage and information about any symptoms you have helps doctors plan the best treatment for you.
We have more information about stages of CLL.
Treatment for CLL
A team of specialists will meet to discuss the best possible treatment for you. This is called a multidisciplinary team (MDT).
Your doctor, cancer specialist or nurse will explain the different treatments and their side effects. They will also talk to you about things to consider when making treatment decisions before you agree (consent) to have treatment.
Active monitoring for CLL
Doctors usually wait until there are signs that CLL is causing symptoms before suggesting you have treatment. There is no evidence that starting treatment before this helps. Treatment can also cause side effects.
Some people with CLL, might not need treatment for many years. Active monitoring (also called watch and wait or active surveillance) is used when you do not need treatment straight away.
It is important to talk to your specialist doctor or nurse. They can help you understand why active monitoring may be the best approach for you.
During active monitoring, your cancer team will:
- check your blood count regularly
- check if you have any symptoms
- provide advice and support
Your cancer team will discuss how often they will meet with you. It is important to attend the appointments. If you develop symptoms, contact your cancer team. Do not wait until your next appointment.
If you need treatment for CLL
Most people who do need treatment are treated with targeted therapy.
Very rarely other cancer treatments used to treat CLL include:
- chemoimmunotherapy
- donor (allogeneic) stem cell transplant
- radiotherapy
- surgery.
You may also have supportive treatments to help control any symptoms caused by CLL, such as infections or anaemia.
You may have some treatments as part of a clinical trial.
We have more information about treatment for CLL.
Your cancer team may also give you advice about preparing for your treatment. This is sometimes called prehabilitation. It helps to improve your fitness and diet and to get you ready mentally before treatment.
Living with 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.
Follow-up appointments are a good time to talk to your cancer doctor or specialist nurse about any concerns you have. Tell them as soon as possible if you have any problems or notice new symptoms between appointments.
We have more information about follow-up care after treatment.
Wellbeing and recovery
Taking good care of yourself can help speed up your recovery after CLL treatment. Even small lifestyle changes may improve your wellbeing and long term health.
Even if you already have a healthy lifestyle, you may choose to make some positive changes after treatment. We have more information on leading a healthy lifestyle after treatment.
More information and advice
We know cancer can affect you physically, emotionally and financially. We have information and advice about different ways cancer might impact you, such as help with:
Getting support when you have CLL
People often have many different feelings during and after CLL treatment. If you have finished treatment, you may feel relieved it has ended but worried about what might happen in the future.
It is important to know where to get support or information if you need it. People often need support even if it has been some time since they finished cancer treatment. But sometimes it is difficult to know who to ask for help.
To find support:
- ask your GP or someone from your cancer team for advice about support in your area
- find cancer support services near you
- call the Macmillan Support Line for free on 0808 808 00 00
- chat to our cancer information specialists online
- visit our Online Community CLL, SLL, HCL forum to talk to people who have been affected by CLL, share your experience, and ask questions.
The HOPE programme
This is a free 6 week self-management course designed to help you develop techniques and strategies when living with or after cancer.
Topics include goal setting, fatigue management, and wellbeing. You can sign up for the online HOPE programme. Or to find out more about face-to-face programmes in your area, email ServiceOpsSupport@macmillan.org.uk.
Other organisations who offer information and support
- CLL Support Association
CLL Support helps CLL patients, their families and their carers through education and access to reliable, relevant and current information. - Blood Cancer UK
Blood Cancer UK is a blood cancer research charity that provides information and support on any type of blood cancer. - Anthony Nolan
Anthony Nolan is the UK’s largest stem cell and bone marrow register.
About our information
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.
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ReferencesBelow 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
Eichhorst B, et al. Robak T, Montserrat E, et al. Chronic Lymphocytic Leukaemia: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow up. Annals of Oncology. Published online October 19 2020 32(1) 23-33. Available from: www.doi.org/10.1016/j.annonc.2020.09.019 [accessed 2023].
Walewska R, Eyre T.A, Bloor A et al. Guideline for the treament of chronic lymphocytic leukaemia. British Society for Haematology 2025. Br J Haematology Vol 207 (6) 2296-2313. Available from: www.doi.org/10.1111/bjh.70100 [accessed August 2026].
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