Chronic lymphocytic leukaemia (CLL)
About 240* people in Ireland are diagnosed with CLL each year.
Signs and symptoms
Learn about the signs and symptoms of CLL. You are more likely to survive cancer if you find it at an earlier stage.
Treatments
There are a number of different treatments available for CLL. Your medical team will explain the best treatment options for you.
What is chronic lymphocytic leukaemia (CLL)?
CLL is a type of leukaemia (cancer of the blood).
Your body has 3 main types of blood cells - red blood cells, white blood cells and platelets.
CLL is usually a slow-growing cancer of lymphocyte white blood cells.
White blood cells help the body to fight infection. CLL stops the white blood cells working properly to fight infection.
CLL also means that the lymphocytes don’t die off naturally at the end of their life span. The cells may build up in your lymph nodes and spleen, causing them to become swollen. They can also build up in your bone marrow, meaning there is not enough space for normal blood cells to develop. This causes problems with fighting infection, carrying oxygen and bleeding.
Many people with slow-growing CLL can live a normal life. Other people experience symptoms that affect their quality of life at different stages of their disease and treatment.
Small lymphocytic lymphoma (SLL)
CLL and SLL are different forms of the same disease - they both affect lymphocytes. The difference between them is where the cancer is mainly found:
- CLL: Most of the cancer cells are in the blood and the bone marrow. The lymph nodes and spleen may be affected too.
- SLL: Most of the cancer cells are in the lymph nodes.
Treatment and care for SLL and CLL are the same. If you have SLL and need more specific information, speak to your doctor or specialist nurse, or you can call our Support Line on 1800 200 700.
What do blood cells do?
There are 3 main types of blood cells:
- Red blood cells carry oxygen to all the tissues in your body.
- White blood cells are involved in fighting infection.
- Platelets form clots which stop you from bleeding.
All blood cells come from cells known as stem cells. These start out as immature cells (blast cells) and then they develop into different types of mature blood cells.
- Lymphoid stem cells develop into lymphocytes. Lymphocytes are white blood cells that fight infection. They are further divided into T-cells, B-cells and NK (natural killer) cells, depending on how they fight infection. CLL affects the B cells.
- Myeloid stem cells go on to form red blood cells, platelets and some types of white blood cells.
New blood cells are normally made in your bone marrow. Bone marrow is the soft spongy tissue that fills the centre of some of your bones.
As blood cells develop, they move out of the bone marrow and into your bloodstream where they do different jobs, such as fighting infection (white blood cells) and carrying oxygen (red blood cells).
As new cells move out of your bone marrow and into your blood, old cells are replaced when needed. With leukaemia, this process of making and replacing blood cells goes wrong.
What increases my risk of CLL?
The cause of CLL is unknown. But there are certain things called risk factors that can increase your chance of developing the disease.
These include:
CLL happens mostly in people aged over 50. More than half of people are aged over 70 years when they are first diagnosed. It doesn’t affect children.
It is more common in men than women.
You have a slightly higher risk of getting CLL if some of your close relatives (e.g. a parent, brother or sister) had it, but the risk is small. Around 1 in 30 people with CLL will have a relative with CLL or a similar B-cell leukaemia or lymphoma.
CLL is most common in white populations. It is less common in people of African origin and rare in Asian populations.
Having a risk factor doesn’t mean you will get cancer. Sometimes people with no risk factors get the disease. If you’re worried or have a family history of CLL, talk to your GP or to one of our cancer nurses. Call 1800 200 700 or visit a Daffodil Centre.
Medical content updated from our 'Understanding chronic lymphocytic leukaemia' booklet (2026). Reviewed by Dr Niamh Appleby, Consultant Haematologist; Fidelma Hackett, Haematology Advanced Nurse Practitioner; Melissa Martin, Haematology Clinical Nurse Specialist.
The 2026 edition was also reviewed by the National Cancer Control Programme's Chronic Lymphocytic Leukaemia Clinical Advisory Group (NCCP CLL-CAG).
Continue reading about chronic lymphocytic leukaemia (CLL)
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*The Irish Cancer Society uses the most up-to-date cancer statistics from the National Cancer Registry Ireland, available on www.ncri.ie
