Chronic myelomonocytic leukaemia (CMML) | Cancer Research UK
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Chronic myelomonocytic leukaemia (CMML)

This page tells you about chronic myelomonocytic leukaemia (CMML). There is information about


What is chronic myelomonocytic leukaemia (CMML)?

Chronic myelomonocytic leukaemia (CMML) is a type of blood disorder in which there are too many monocytes in the blood. Monocytes are a type of white blood cell. 

As CMML is a chronic disease it develops slowly. Treatment can control it for a long time and the main aim of treatment is to try to manage symptoms. The only way to get rid of CMML completely is to have a stem cell transplant but unfortunately this treatment is not suitable for everyone.

Although it has leukaemia as part of its name, the World Health Organisation (WHO) classes CMML as one of a group of blood conditions called myeloproliferative/myelodysplastic neoplasms. Myeloproliferative means that the bone marrow makes too many blood cells. Myelodysplastic means that the blood cells are abnormal and not fully mature.

The bone marrow is the soft inner part of some of our bones. It makes blood cells. Stem cells in the bone marrow make immature blood cells. The immature cells go through different stages of development before they are released into the blood as fully developed blood cells. The bone marrow makes different types of blood cells, including

  • Red blood cells to carry oxygen around our bodies
  • White blood cells to fight infection
  • Platelets to help the blood clot

The diagram shows how the different types of cells develop from a single blood stem cell.

White blood cells called monocytes help the body to fight infection. In CMML the bone marrow produces abnormal monocytes. They are not fully developed and can’t work normally. These abnormal blood cells either stay in the bone marrow or are destroyed before they get into the bloodstream. As the CMML develops, the bone marrow becomes full of the abnormal monocytes. These immature blood cells then spill out into the bloodstream.

Because the bone marrow is full of the immature cells it can’t make enough of the other types of blood cells. The low numbers of normal blood cells in the bloodstream eventually cause symptoms.


Types of CMML

There are 2 types of CMML. They are called type 1 and type 2. The type tells you how many abnormal myeloid cells (blasts) you have in your blood samples.

  • Type 1 CMML means that fewer than 5 out of every 100 white blood cells (5%) in your blood are blasts
  • Type 2 CMML means that between 5 out of every 100 white blood cells (5%) and 20 out of every 100 cells (20%) are blasts

Knowing your type of CMML helps your doctor to decide on the best treatment for you.

CMML can develop into an acute myeloid leukaemia (AML). If more than 20 out of every 100 white blood cells are blasts (more than 20%) the CMML has become AML. Doctors call this transformation. This happens in between 15 and 30 out of every 100 people with CMML (15 to 30%). Transformation may happen after a few months or after several years.


Symptoms of CMML

CMML usually develops slowly and doesn’t cause symptoms at first. When it does start to cause symptoms they include

  • Tiredness (fatigue)
  • Infections that don’t get better
  • Bruising or bleeding easily – including nosebleeds or bleeding gums
  • Abdominal discomfort from a swollen spleen
  • Loss of appetite

Risks and causes of CMML

We don't know the cause of most cases of CMML but there are some risk factors that may increase your risk of developing it. A risk factor is something that may make you more likely to develop a particular condition or disease.

Your risk of developing CMML increases with age. It most commonly develops after the age of 60. And it is more common in men than women.

If you have had treatment for cancer you are at an increased risk of developing CMML.

Researchers have found that around half of the people who have CMML (50%) have a change in a gene called TET2. The TET2 gene makes a protein that controls how many monocytes the stem cells make. Between 10 and 30 out of 100 people (10 to 30%) have a change in a gene called RAS. The change makes the cells multiply uncontrollably.

We need more research to find out what causes the changes in these genes.

There are a number of other gene changes that people with CMML may have but they are uncommon.


Diagnosing CMML

Most people are diagnosed because doctors find abnormal monocytes during a blood test for something else. Your doctor may then arrange a number of tests for you. They include

The links above take you to pages about these tests.

The blood tests show how many blood cells you have and whether they are normal. You also have tests to look at the bone marrow cells. Your doctor may do tests to look for anything unusual in the chromosomes of the CMML cells. Chromosomes contain the genetic material inside cells. These tests are called cytogenetics (pronounced sigh-toe gen-et-ics).


Treatment for CMML

If you have no or few symptoms you may not need treatment at first. Instead you will have regular check ups including blood tests.

The type of treatment you need depends on

  • The type of CMML you have
  • Whether you have symptoms
  • Your age
  • Whether you have any other medical conditions

Treatments for CMML include

Supportive treatment

Supportive treatment aims to help control the symptoms of CMML. Most people need this type of treatment at some point. The supportive treatment you need depends on the type of symptoms you have. You may need a combination of treatments.

You may have blood transfusions if your red blood cells are low. And if your platelets are low you will have a drip of a clear fluid containing platelets.

Having a lot of blood transfusions can cause a build up of iron in your body. Red blood cells contain iron and your body stores this. But too much iron in your body can damage your heart and liver. To stop this, you may need to take medicines to get rid of the extra iron.

Growth factors are drugs that encourage your bone marrow to make more blood cells. We know from research that this can reduce the number of blood transfusions that people need. Erythropoetin is a growth factor that increases the number of red blood cells. So you may have this if your red blood cell level is low. G-CSF is a growth factor that increases the number of white blood cells. So you may have this if your white blood cell levels are low.

You have both of these drugs as injections just under the skin (subcutaneously).

You may also need to take antibiotics to treat infections.


Chemotherapy is the main treatment for most people with CMML. It uses cell killing (cytotoxic) drugs to destroy the immature monocyte cells. The drugs work by disrupting the growth of cells and stopping them from dividing. You may have chemotherapy as a tablet, an injection just under your skin, or as an injection into a vein. You may have just one drug or a combination of drugs.

The type of chemotherapy you have depends on your type of CMML and your general health. If you have just been diagnosed your first chemotherapy is likely to be cytarabine, hydroxyurea or azacitidine.

If you are at high risk of developing AML you may have chemotherapy similar to that used to treat AML. You can find more information about these treatments in the chemotherapy for AML section.

Donor stem cell transplant

In a donor stem cell transplant you have a very high dose of chemotherapy. You may also have total body irradiation (TBI). These treatments destroy the cells in your bone marrow. This treatment is very intensive and may get rid of the CMML completely but it is not suitable for everyone. 

After the high dose treatment you have stem cells from a donor through a drip into your bloodstream. The stem cells make their way into the bone marrow and start to make normal blood cells. It takes from a few days to a few weeks for the numbers of blood cells to become normal. During this time you will need blood and platelet transfusions and are at a high risk of developing infections. So your doctor and nurses will give you antibiotics and anti viral drugs to try to prevent them.

You can read all about stem cell transplants in the cancer treatment section. This treatment is very intense and has risks. You can only usually have it if you are under 60 and are in reasonably good health, apart from your CMML.

To be able to have this treatment you need a stem cell donor. The donor is someone whose stem cells match yours. The most suitable donor is usually a close relative such as a brother or sister. You can read about how stem cells are matched on the page about how blood is matched for a transplant.


Newer treatments

Doctors and researchers are looking into a number of other treatments for myeloproliferative / myelodysplastic disorders. They are testing a new cancer drug treatment called decitabine. This is similar to azacitidine. They are also looking at different ways of using azacitidine.

You can find information about research trials looking at treatments for CMML on our clinical trials database. Type ‘cmml’ into the search box. Tick the boxes for closed trials and results if you want to include all the trials.


Coping with CMML

Coping with a rare condition can be difficult, both practically and emotionally. Being well informed about your condition and its treatment can help you to make decisions and cope with what happens.

The symptoms of CMML often mean that you may find it hard to do everyday things. Talk to your doctor or nurse about any symptoms you have. There may be supportive treatments that can help you. You may also feel better if you

  • Eat a healthy well balanced diet
  • Do some exercise – after checking with your doctor
  • Rest when you are tired

If you get tired easily, try to work out your priorities each day. Talk to your family and friends and ask for any help you need. You can find tips about coping with tiredness in the fatigue and cancer section.

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Updated: 22 February 2014