Stages (phases) of chronic myeloid leukaemia (CML)

When your doctors have all your test results, they know how far your chronic myeloid leukaemia (CML) has developed.

In most types of cancer, this is called staging. The stage of your cancer usually describes the size of your cancer and how far it has spread. 

CML is slightly different. Doctors use 3 groups to describe your CML. But they call the groups phases rather than stages. 

The 3 phases are:

  • chronic phase
  • accelerated phase
  • blast phase

How do doctors work out your phase of CML?

Different groups of CML experts have slightly different definitions of the 3 phases of CML. We have based our information below on the European LeukaemiaNet definition. This is the definition that researchers use in most of the recent CML clinical trials.

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

Your doctor looks at all your test results. In particular, they look at the number of immature white blood cells called blasts. They do a blood test and a bone marrow test to find this out.

The doctors also look at the number of white blood cells and platelets in your blood. And they examine the leukaemia cells to look for chromosomal changes (abnormalities).

Chronic phase

The chronic phase is when the leukaemia is most stable and still developing slowly. Most people are in this phase at diagnosis.

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

In chronic phase CML:

  • your blood and bone marrow tests mostly show mature, fully functioning blood cells and you only have occasional immature (blast) cells 

You might also have:

  • a lower than normal level of red blood cells Open a glossary item (anaemia)
  • a higher or lower level of platelets Open a glossary itemthan is normal

Accelerated phase

In the accelerated phase, you have more obvious symptoms. You might notice that you:

  • feel more tired than usual
  • have lost weight
  • have a swollen tummy (abdomen) or have discomfort to the left of your stomach, under your ribs - this is due to an enlarged spleen

In accelerated phase CML:

  • your blood and bone marrow tests show a higher number of immature (blast) cells than in the chronic phase

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). 

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

In blast phase CML:

  • many blast cells fill your bone marrow and there are also more blast cells in your blood

The leukaemia cells might have spread to other organs.

  • Chronic myeloid leukaemia: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up
    A Hochhaus and others
    Annals of Oncology (2017) Volume 28, Supplement 4, Pages 41– 51

  • Essential haematology (8th Edition)
    A. Hoffbrand and D.Steensma
    Wiley-Blackwell, 2019 

  • Chronic myeloid leukaemia
    J Cortes and others
    Lancet 2021, Volume 398, issue 10314, pages 1914-1926

  • European LeukemiaNet 2020 recommendations for treating chronic myeloid leukemia
    A. Hochhaus and others
    Leukemia (2020) Volume 34, pages 966–984

  • A British Society for Haematology Guideline on the diagnosis and management of chronic myeloid leukaemia
    G Smith and others
    British Journal  of  Haematology, 2020, volume 191 pages 171–193

Last reviewed: 
14 Aug 2022
Next review due: 
14 Aug 2025

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