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What is CLL?

About Chronic Lymphocytic Leukaemia (CLL)

Chronic Lymphocytic Leukaemia is usually a slow-growing blood cancer that prevents lymphocytes from dying off naturally at the end of their life span.

CLL cells shown in purple

What causes CLL?

It’s not clear what causes CLL. It is more common in people over the age of 60.

How does it develop?

The affected cells may build up in the lymph nodes and spleen, causing them to become swollen.

They can also build up in the bone marrow which is the place where blood cells are made.

If they build up in the bone marrow there is not enough space for normal blood cells to develop which causes problems with fighting infection, carrying oxygen and blood clotting.

Many people can live a normal life, but for others the disease can compromise their ability to live fully at different stages of their disease.

This video from our friends in Leukemia & Lymphoma Society of Canada (LLSC) helps explain the CLL Journey

What are the other main types of Leukaemia?

The other main types of leukaemia are

  • Acute lymphocytic leukaemia (ALL)
  • Chronic myeloid leukaemia (CML)
  • Acute myeloid leukaemia (AML)


In a small number of people the leukaemia can change and start to grow more quickly. When leukaemia changes from one type to another, it is called transformation.

Transformation is unusual and doesn’t happen for most people with CLL.

Transformation can be found by a blood test that shows a high number of leukaemia cells. Sometimes, the first sign of transformation is when a person has more symptoms or a sudden increase of symptoms.

In about 10% of people (1 out of 10), CLL may change into another type of leukaemia called prolymphocytic leukaemia (PLL).

In less than 10% of people, CLL may develop into a faster growing disease, a rare type of non-Hodgkin lymphoma (cancer of the lymphatic system) called Richter’s syndrome.

A condition called autoimmune haemolytic anaemia may develop as a complication of CLL or its treatment with the drug fludarabine. The risk of developing skin cancer is much higher as well.

See: Complications of CLL for more information 

What is SLL?

SLL is Small Lymphocytic Lymphoma. It is similar to Chronic Lymphocytic Leukaemia – the difference is where the cancer is mainly found.

In CLL most of the cancer cells are in the blood and the bone marrow. The lymph nodes and spleen may be affected too.

In SLL mostly of the cancer cells are in the lymph nodes, with a smaller amount in the blood.

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CLL Ireland today

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Information about CLL

We’ve put together a set of resources to help you on your journey with CLL. Click to find out more!

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