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Chronic lymphocytic leukaemia (CLL)

Chronic lymphoblastic leukaemia (CLL) is a blood cancer that stops the white blood cells of your immune system growing properly.

It involves blood cells called B lymphocytes that develop from stem cells in your bone marrow.

Before these cells mature into lymphocytes, they’re called lymphoblasts (immature lymphocytes). Your body needs to make new lymphocytes – but when you have CLL, this process doesn’t work properly. Instead, the immature cells grow too quickly and cannot function properly. Over time, they accumulate in the lymphatic system and may cause large, swollen lymph nodes. They also fill the bone marrow, reducing the number of normal white blood cells, red blood cells and platelets that can be made. 

CLL is a chronic condition that usually develops very slowly – many people don’t need treatment for months or years. However, some people may need to have treatment straight away.

CLL is the most common type of leukaemia for adults in the UK.

More information on CLL is available on the Blood Cancer UK and Leukaemia Care websites.

CLL facts

Chronic lymphoblastic leukaemia

Cell type: 
B Lymphocytes, a type of white blood cell

3,824 / year in the UK

UK transplants:
14 in 2019

More common in people over 70

Chemotherapy or immunotherapy (when drugs stimulate the immune system) may be needed but not always straight away

Other information:
CLL progresses very slowly and very few people will need a stem cell transplant


CLL and stem cell transplants    

You will normally only be offered a bone marrow or stem cell transplant if your CLL hasn’t responded to initial treatment, or if your doctors think it’s unlikely to.

Most transplants for CLL are allograft transplants – when stem cells are donated to you by someone else.

It only happens very rarely, but some people with CLL have an autologous transplant – when doctors use your own stem cells.

Information published: 11/02/21
Next review due: 11/02/24

Related links

Preparing for a stem cell transplant

Having a stem cell transplant

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