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The staging of chronic myeloid leukaemia (CML) is described in phases. The phase of your CML helps your doctor to decide which treatment you need.

What staging means

When your doctors have all your test results, they know how far your leukaemia has developed. This is called staging. The staging in chronic myeloid leukaemia (CML) is described in 3 phases. These are the chronic phase, accelerated phase and the blast phase.

Staging can be quite complicated. Ask your doctor or specialist nurse if you are not sure which phase your CML is.

How doctors work out your phase

Your doctor looks at all your test results. In particular, they look at the number of immature white blood cells called blasts. This is measured with a blood test and a bone marrow test.  

Chronic phase

The chronic phase is when the leukaemia is most stable and still developing slowly.

About 9 out of 10 people (90%) are in chronic phase when they are diagnosed. Some people are diagnosed by chance and have no symptoms.

You might have symptoms that are mild and vague. You might feel tired and lose a little weight. Your tummy (abdomen) might be swollen due to an enlarged spleen.

The number of white cells in your blood might be raised, as well as the number of platelets.

In this phase, typically fewer than 1 in 10 (10%) of the blood cells in your bone marrow are immature white blood cells known as blasts.


Biological therapy is the most common treatment for this phase using a drug called imatinib (Glivec). Most people respond well to this treatment and the CML can stay under control for several years.

Imatinib may not work for some people, or it stops working after a period of time. In this situation, your doctor might recommend another type of biological therapy called nilotinib (Tasigna). 

Other treatment options include:

  • chemotherapy
  • intensive treatment with bone marrow or stem cell transplant

A transplant is not suitable for everyone. You have to be reasonably fit and well to cope with the treatment and its side effects.

For CML, you usually have a transplant using the stem cells or bone marrow of a donor. This is called an allogeneic transplant.

Accelerated phase

In the accelerated phase, you have more obvious symptoms. You might notice that you feel more tired than usual. You may lose weight. Your tummy (abdomen) might be swollen due to an enlarged spleen. This might give you an uncomfortable or painful feeling to the left of your stomach, under your ribs.

In this phase between 10% and 30% of the blood cells in your bone marrow are immature blasts.


The treatment for the accelerated phase depends on the treatment you have already had. Imatinib (Glivec) is normally the first choice unless you have already had it in the chronic phase.

Some people who have imatinib for the first time in the accelerated phase might have a good response to treatment. It might put their CML back into the more stable chronic phase for a time.

You might have treatment with biological therapy if you have already had imatinib. For example, nilotinib (Tasigna) or dasatinib (Sprycel).

Other treatment options include chemotherapy. Or your doctor might recommend more intensive treatment using a bone marrow or stem cell transplant. This is more likely if you are younger and fairly fit and well. 

Blast phase

The blast phase is also called the acute phase, blast crisis or blast transformation. This is when the leukaemia transforms into an acute leukaemia (usually acute myeloid leukaemia). 

In this phase many blast cells fill the bone marrow. There are also more blast cells in the blood.

You can feel quite unwell and your symptoms could be troublesome. Your spleen is enlarged.

In this phase, more than 30% of the blood cells in your bone marrow or blood are immature blast cells. The leukaemic cells might have spread to other organs.


Your doctor might suggest treatment with imatinib (Glivec) if you haven’t had it before. Or you might have other biological treatments, such as nilotinib or dasatinib.

Other options include:

  • chemotherapy with a combination of drugs that’s usually used for acute leukaemia
  • a bone marrow or stem cell transplant

You might have treatment to relieve symptoms. For example, radiotherapy to shrink an enlarged spleen. Or radiotherapy to reduce pain in the bones.

Information and help

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