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:

  • chronic phase
  • accelerated phase
  • 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. Most people are in this phase when they are diagnosed.

Not everyone has symptoms in this phase. If you do have symptoms they might be 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.


Targeted cancer drugs called tyrosine kinase inhibitors are the most common treatment. There are several TKI's available and most people start with a TKI 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, you will be offered one of the other TKI's.

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.

If you have already had imatinib you might be treated with a different drug. Other drugs include nilotinib (Tasigna), dasatinib (Sprycel), bosutinib (Bosulif) and ponatinib (Iclusig). 

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 and have failed to respond to TKI treatment. 

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 a TKI and if the response is not adequate then 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.

Last reviewed: 
09 May 2019
  • Chronic Myeloid Leukaemia: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow up

    A. Hochhaus and others

    Annals of Oncology, 28, (Supplement 4) pages 41-51, 2017

  • Essential haematology
    Hoffbrand and Moss, 7th Edition, 2016

  • Chronic myeloid leukaemia
    Professor J F. Apperley
    The lancet. Volume 385, Issue 9976, 11–17 April 2015, Pages 1447–145

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