Chronic lymphocytic leukaemia (CLL)

Chronic lymphocytic leukaemia (CLL)

What is chronic lymphocytic leukaemia?

Chronic lymphocytic leukaemia (CLL) is a blood cancer. It is also known as chronic lymphatic leukaemia.

Blood is made up of three main types of cells:

  • white blood cells – fight infection
  • red blood cells – carry oxygen around the body
  • platelets – help the blood to clot.

CLL develops when the body makes too many abnormal white blood cells. Because they live too long or multiply too quickly, there will be large numbers circulating in the blood. They crowd out normal white blood cells and don’t fight infection themselves, so there can be a higher risk of infection (neutropenia).

As leukaemia progresses, the bone marrow fills with leukaemia cells and there is less room for healthy red cells and platelets to be produced. This may cause various health problems, such as anaemia (from too few red cells) or bleeding or bruising (from thrombocytopenia, too few platelets).

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What is the difference between chronic and acute leukaemia?

While all types of leukaemia start in the bone marrow and affect white blood cell production, they are grouped according to which type of white blood cell is affected (lymphoid or myeloid), whether there are abnormalities in the bone marrow, and how quickly the disease develops.

Chronic leukaemia usually affects partly immature cells, appears gradually, and develops slowly over months to years.

Acute leukaemia affects fully immature cells, occurs suddenly, and develops quickly. See Acute Leukaemia for more information.

Who gets CLL?

Each year in Australia, about 3700 people are diagnosed with a form of leukaemia, and more than 1700 of these cases are chronic leukaemia.

CLL is the most common type of chronic leukaemia, with about 1400 people diagnosed each year. CLL is twice as likely to occur in men than in women and is very rare in children.

What causes CLL?

Chronic leukaemia is caused by changes to one or more of the genes (DNA) that control the growth and development of blood cells. These changes happen over time, but it is not known why they occur in some people and not others. The exact cause of CLL is not yet understood.

Some people have genetic abnormalities that can lead to CLL. These genetic defects are not usually inherited, but there are rare cases where CLL may occur more commonly in families. If you are worried about this, talk to your doctor, who may refer you to a genetic counsellor.

Blood cells and leukaemia cells

Blood is pumped around your body to provide oxygen and nutrients to your tissues, and to remove waste products. It is made up of blood cells carried in a clear fluid called plasma. The three main types of blood cells have specific functions: 

  • red blood cells – carry oxygen around the body
  • white blood cells – fight infection
  • platelets – help the blood clot

All three types of blood cells have a limited life span and need to be continually replaced. Most are made in the bone marrow, which is the spongy part in the centre of the bones.

The bone marrow contains stem cells. These are unspecialised blood cells that first develop into immature cells known as blast cells. Normally, the blast cells then become mature red or white blood cells or platelets and carry out their set functions.

There are two families of stem cells:

  • myeloid stem cells – develop into myeloblast cells and then into red blood cells, most types of white blood cells, and platelets
  • lymphoid stem cells – develop into lymphoblast cells and then into lymphocytes, which are a type of white blood cell.

If myeloblast or lymphoblast cells do not mature properly or if there are too many in the blood, it can cause leukaemia.

How blood cells are made

In leukaemia, blast cells never develop into mature white blood cells. These abnormal blast cells are also called leukaemia cells.


This information was last reviewed in March 2018
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