Chronic myeloid leukaemia (CML)

What is chronic myeloid leukaemia?

Chronic leukaemia is a blood cancer that develops when the body makes too many abnormal white blood cells (blast cells). These abnormal blast cells are known as leukaemia cells.

Because leukaemia cells live too long or multiply too quickly, large numbers of them circulate in the blood. They crowd out normal white blood cells and, because they don’t fight infection, they increase the risk of infection.

As leukaemia progresses, the bone marrow fills with leukaemia cells and there is less room for healthy red cells and platelets. This may cause various health problems, such as tiredness, dizziness, bleeding problems and bruising.

Learn more about:

• Is it different to acute leukaemia
• What are CML and CLL?
• Who gets CML?
• What causes CML?
• The blood
• The lymphatic system

Is it different to 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, whether there are abnormalities in the bone marrow, and how quickly the disease develops.

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

Acute leukaemia affects undeveloped cells, occurs suddenly, and develops quickly. 

Learn more about acute lymphoblastic leukaemia and acute myeloid leukaemia.

What are CML and CLL?

CML and CLL are the two main types of chronic leukaemia. The difference between them is in the type of white blood cell that is affected.

Chronic myeloid leukaemia (CML)

In CML, the body has too many of the white blood cells known as granulocytes. The granulocytes are part of the myeloid family of blood cells. This disease is sometimes called chronic granulocytic leukaemia.

Learn how CML is diagnosed and treated.

Chronic lymphocytic leukaemia (CLL)

In CLL, the body has too many of the white blood cells known as lymphocytes. The lymphocytes are part of the lymphoid family of blood cells. This disease is also called chronic lymphatic leukaemia.

Learn how CLL is diagnosed and treated.

Who gets CML?

Each year in Australia, about 3900 people are diagnosed with a form of leukaemia, and more than 1900 of these cases are chronic leukaemia.

About 320 people are diagnosed with CML annually. It is slightly more common in men than in women and is rare in children.

What causes CML?

Chronic leukaemia is caused by changes to one or more of the genes 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. Exposure to some chemicals or high doses of radiation has been linked to developing leukaemia, but this doesn’t explain most cases.

Most people with CML have a genetic abnormality known as the Philadelphia chromosome. This abnormality is not inherited – it happens during your lifetime and is present only in the abnormal blood cells.

The blood

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.

There are three main types of blood cells: white blood cells, red blood cells, and platelets. Each type has a specific job to do:

	White blood cells – fight infection.
	Red blood cells – carry oxygen around the body.
	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.

Bone marrow contains blood stem cells. These are unspecialised blood cells that first turn into immature cells known as blast cells. Normally, the blast cells become mature white or red blood cells or platelets. If white blood cells do not mature properly or if there are too many in the blood, it can cause leukaemia.

There are two families of blood stem cells: lymphoid and myeloid (see diagram below). These lead to different types of white blood cells and can be affected by different types of leukaemia.

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

Blood cell families

Stem cells divide into two families (lymphoid or myeloid), then become immature cells (lymphoblast or myeloblast cells). If cells are normal, they develop into different kinds of mature blood cells.

The lymphatic system

The lymphatic system works with the white blood cells to protect the body against infection. A large network of thin tubes (lymph vessels) carries a clear fluid called lymph.

The lymph travels to and from areas of lymph tissue, including the lymph nodes, spleen and liver. When leukaemia causes abnormal white blood cells to build up, the lymph tissue becomes swollen.

Diagram of the lymphatic system