What is chronic myeloid leukaemia?

Chronic myeloid leukaemia (also called CML or CML leukemia) is a rare type of cancer. It causes the body to make too many white blood cells.

About 750 people in the UK are diagnosed with CML each year. It can affect people at any age, but it is more common as people get older.

We have separate information about other types of leukaemia.

How chronic myeloid leukaemia develops

CML usually develops very slowly, which is why it is described as a chronic leukaemia. For most people, it can be well controlled, and they will live a normal life-span.

Blood cells are made in the bone marrow. This is a spongy material found inside our bones. Every blood cell grows from a stem cell in the bone marrow. Normally, the stem cells make an early stage of the blood cell called a blast. These blasts develop into healthy blood cells.

There are two types of blood stem cell:

  • lymphoid stem cells – make a type of white blood cell called lymphocytes
  • myeloid stem cells – make red blood cells, platelets and all other types of white blood cell.

MACD261 How blood cells divide

CML is a cancer of the white blood cells. It develops when some white blood cells start behaving abnormally.

We have information about changes to genes and chromosomes in CML. This will help you understand the sections about having tests and treatment. 

The information is quite technical, so you might need to read it more than once. Do not worry if it is too much to take in. It is fine to skip it and come back to it another time.

Symptoms of chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) develops slowly and many people do not have symptoms in the early stages. Sometimes it is discovered by chance when a blood test is done before an operation or as part of a routine health check.

If there are symptoms in the early stages of CML, they are usually mild and develop gradually. The symptoms can be confused with the symptoms of more common illnesses, such as flu.

We have more information about the symptoms of leukaemia.

Causes of chronic myeloid leukaemia

It is not clear why people get chronic myeloid leukaemia (CML). There are some things called risk factors that might increase the risk of developing CML.

We have more information about risk factors and causes of CML.

Diagnosis of chronic myeloid leukaemia

If your GP suspects you have chronic myeloid leukaemia (CML), they will refer you to the hospital to see a haematologist. This is a doctor who specialises in diagnosing and treating blood problems.

The haematologist will ask you about any illnesses or health problems you have had. They will do blood tests, and examine you if your spleen is enlarged.

We have more information about how CML is diagnosed. This includes information about the tests the haematologist will do.

Chronic myeloid leukaemia phases

Chronic myeloid leukaemia (CML) develops slowly. There are three possible phases of CML:

  • the chronic phase
  • the accelerated phase
  • the blast phase.

Most people are diagnosed when CML is in the chronic phase.

Treatment of chronic myeloid leukaemia

A team of specialists will meet to discuss the best possible treatment for you. This is called a multidisciplinary team (MDT).

Your cancer doctor or specialist nurse will explain the different treatments and their side effects. They will also talk to you about certain things to think about when making treatment decisions.

The aim of treatment is to put CML into remission. Treatments used can include the following:

  • Tyrosine kinase inhibitors (TKIs)

    Most people with CML are treated with targeted therapy tablets called tyrosine kinase inhibitors (TKIs).

  • Chemotherapy

    If you have a very high level of white blood cells in your blood when you are first diagnosed, you may be given chemotherapy tablets for a few days.

  • Stem cell transplant

    If TKI treatment does not work, or if you are diagnosed in the blast phase, your doctors may suggest chemotherapy and a stem cell transplant.

  • Interferon alpha

    Interferon alpha is occasionally given in the chronic phase. Doctors may also use it for women who are pregnant or want to become pregnant.

  • Leukapheresis

    Some people have a very high number of white blood cells in their blood when they are diagnosed with CML. Doctors can treat this using a process is called leukapheresis.

  • Clinical trials

    You may be invited to take part in a clinical trial of a new treatment for CML.

We have more information about treatment for CML.


Some cancer treatments can affect fertility or harm a developing baby. Because of this you may be advised to use contraception to prevent a pregnancy. If you want to have children or think you may in the future, talk to your doctor about this as soon as possible. They can talk to you about the possible options for planning your treatment.

We have more information about fertility for men and fertility for women.

Living with chronic myeloid leukaemia

Follow-up and monitoring

If you are being treated with a TKI, when you first start treatment, you will need to go to the clinic every 1 to 2 weeks. As time goes on you will not need to go as often. Eventually, you may only need a check-up every 3 to 6 months. We have more information about monitoring response to TKI treatment.

If you have a different treatment, your doctor or nurse will tell you how often you will have appointments.


Most people with CML live a normal life-span. To help you stay as well as possible, you may want to make changes to your lifestyle. Even if you had a healthy lifestyle before your diagnosis, you may want to focus more on making the most of your health.

A healthy lifestyle does not have to be difficult or expensive. It is about making small changes to the way you live. This will improve your health and sense of well-being. It will also lower your risk of getting other illnesses and some other cancers.

When planning changes, you need to take any side effects of treatment into account. Try not to do too much, too soon.

Understanding more about CML and its treatment can help you cope. It means you can discuss treatment, tests and check-ups with your doctors and nurses, and be involved in making decisions. This can make you feel more confident and give you back a feeling of control. Here are some things to consider:

  • Get involved in your healthcare

    This includes taking your medicines as prescribed and always going to your hospital appointments. If you have any problems or notice any new symptoms between your appointments, let your doctor know as soon as possible.

  • Self-help and support groups

    Talking about your feelings can help reduce stress, anxiety and isolation. Self-help or support groups offer a chance to talk to other people who may be in a similar situation and facing the same challenges as you.

  • Online support

    There are online support groups, social networking sites, forums, chat rooms and blogs for people affected by leukaemia. You can use these to ask questions and share your experience. You can find details of our Online Community below.

Getting support

Everyone has their own way of dealing with illness and the different emotions they experience. You may find it helpful to talk things over with family and friends or your doctor or nurse. 

The organisations below offer information and support:

  • Anthony Nolan
    Anthony Nolan is the UK’s largest stem cell and bone marrow register.
  • Leukaemia CARE
    Leukaemia CARE provides care and support to patients, their families and carers whose lives have been affected by leukaemia, lymphoma or a related blood disorder.
  • Blood Cancer UK
    Blood Cancer UK is a blood cancer research charity that provides information and support on any type of blood cancer.

Macmillan is also here to support you. If you would like to talk, you can:

About our information


  • References

    Below is a sample of the sources used in our chronic myeloid leukaemia (CML). If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    European Leukemia Net. Recommendations for the management of chronic myeloid leukemia. 2013.

    Hoffbrand V, and Moss P. Hoffbrand’s essential haematology. 7th edition. 2016.

    National Institute for Health and Care Excellence. Leukaemia (chronic myeloid) – dastatinib, nilotinib and standard dose imatinib for the first-line treatment of chronic myeloid leukaemia (part review of technology appraisal guidance 70). April 2012.

    National Institute for Health and Care Excellence. Technology appraisal guidance. 401/426/425.

    DeVita V, Lawrence T and Rosenberg S. 2016. Lymphomas and leukemias. From Cancer: principles and practice of oncology.


  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Anne Parker, Consultant Haematologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Reviewed: 31 July 2017
Reviewed: 31/07/2017
Next review: 31 January 2020
Next review: 31/01/2020

This content is currently being reviewed. New information will be coming soon.