Myelofibrosis (MF)

Myelofibrosis (MF) is a rare condition affecting the bone marrow. Bone marrow is where our blood cells are made. In MF, scar tissue builds up inside the bone marrow and blood cells aren’t made properly. Other parts of the body, usually the spleen and liver, begin to make blood cells.

At first, MF may not cause any symptoms. Sometimes the spleen may grow in size as it starts to make blood cells. This can cause discomfort in the tummy and feeling full when eating.

To diagnose MF, your doctor may suggest a blood test, or you may have a bone marrow test. This is when a sample of bone marrow cells is taken from your back or hip bone to be examined by a doctor.

If you don’t have any symptoms of MF, you may not need treatment straight away. You may have chemotherapy (anti-cancer drugs). If you have a low red blood cell count (anaemia), you may have a blood transfusion.

Other treatments include:

  • targeted therapies
  • steroids
  • surgery to remove the spleen
  • radiotherapy to shrink the spleen
  • a stem cell transplant.

Once treatment has finished you will have regular blood tests and check-ups.

Bone marrow

Bone marrow is part of the immune system, which protects us from infection and disease. The marrow is in the spongy material found inside bones. This is where stem cells are made. Stem cells are blood cells at their earliest stage of development. All blood cells grow from stem cells. The bone marrow makes millions of blood cells every day. The three main types of blood cells are:

  • red blood cells, which carry oxygen around the body 
  • white blood cells, which fight infections
  • platelets, which help blood to clot to prevent bleeding.

What is myelofibrosis (MF)?

Myelofibrosis is a rare condition that affects the bone marrow. In MF, scar tissue builds up inside the bone marrow and blood cells aren’t made properly. It can affect people at any age, including children, but it's most common in people over 50.

MF can occur in people who haven’t any history of problems with their bone marrow. This is called primary myelofibrosis. MF can also develop in people who have essential thrombocythaemia (ET) or polycythaemia vera (PV). This is called post-ET myelofibrosis or post-PV myelofibrosis.;

These are all called myelofibrosis as they behave in the same way.

People with MF may have low levels of one or more types of blood cells. If the bone marrow becomes scarred (fibrosed), it may make fewer blood cells. Some people with MF have too few of some types of blood cells and too many of another type.

To make up for fewer blood cells being made in the bone marrow, other parts of the body, usually the spleen and liver, begin to make blood cells. As the spleen begins to make blood cells, it grows in size.

The enlarged spleen may ‘hold on’ to blood cells, instead of releasing them into the blood. The spleen may also destroy blood cells. This can reduce the numbers of blood cells in the blood.

Signs and symptoms of MF

At first, MF may not cause any symptoms. Some people are diagnosed with MF when they have a blood test for another reason. When symptoms do develop, they are most often due to having too few blood cells or an enlarged spleen.

Possible symptoms include:

  • repeated infections
  • shortness of breath
  • fevers and night sweats
  • weight loss
  • tiredness.

Sometimes other symptoms develop, such as gout (inflammation in the joints). This is due to complications that MF can cause.

Bleeding or bruising

Very occasionally MF can cause abnormal bleeding. This can cause symptoms such as:

  • nosebleeds
  • bruising
  • abnormal vaginal bleeding
  • bleeding gums.

Enlarged spleen

The spleen sits on the left side of the tummy (abdomen) just under the ribs and is normally about the size of a fist. It is involved in breaking down red blood cells. MF can cause the spleen to grow bigger than normal. Symptoms of an enlarged spleen include discomfort on the left side of the tummy and quickly feeling full when eating.

Diagnosis of MF

MF is usually diagnosed by a haematologist (a specialist in blood disorders). The diagnosis may be suspected from the results of a routine blood test called a full blood count. This test counts the number of red blood cells, white blood cells and platelets in the blood.

Tests and investigations that may be done to confirm a diagnosis of MF include:

Blood tests to check for gene changes

Blood tests are done to check for a change (mutation) in genes. Changes in some genes can cause MF. These changes in genes happen during the person's lifetime. It isn't something you’re born with and you can’t pass it on to your children.

JAK2 test

This blood test checks for a change in a gene called JAK2. This gene helps control how many blood cells are made.

CALR blood test

Blood tests might also check for a change in another gene called calreticulin (CALR).

MPL blood test

This blood test looks for a mutation in a gene called MPL.

Bone marrow sample (biopsy)

Your doctor may want to take a sample of bone marrow (biopsy) to examine under a microscope (see diagram below). The sample is usually taken from the back of your hip bone (pelvis). You will be given an injection of local anaesthetic to numb the area. The doctor will then pass a needle through the skin into the bone and draw a small sample of liquid marrow (bone marrow aspirate) into a syringe. 

After this, the doctor will also take a small core (piece) of marrow from the bone (a trephine biopsy). Both samples will be looked at later under a microscope.

A bone marrow sample being taken
A bone marrow sample being taken

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The test can be done on the ward or in the outpatients department. The whole procedure takes about 15 to 20 minutes. It may be uncomfortable when the marrow is drawn into the syringe, but this should only last for a few seconds. 

You may feel bruised and have an ache for a few days after the test. This can be eased with mild painkillers.

Other tests and investigations may also be done, such as scans and x-rays. Your doctor or nurse will explain these to you.

Treatment of MF

Treatment of MF aims to control any symptoms you have. If you don’t have symptoms you may not need any treatment for a while. In this case, your haematologist will monitor your condition regularly. If you develop any symptoms between appointments, let your specialist know.

If you do have symptoms there are different treatments that may be used, but not all treatments are suitable for everyone. Your haematologist will talk about this with you.

Blood transfusion

If you have symptoms caused by a low red blood cell count (anaemia), you can have blood transfusions. Usually it is possible to have a blood transfusion as a day patient but you may need to stay in hospital overnight. You can usually have blood transfusions as often as needed.


Chemotherapy is the use of anti-cancer (cytotoxic) drugs to destroy cancer cells. It may be used to treat MF if the symptoms are severe.

Chemotherapy can help reduce the size of the spleen and the liver, and can help control other symptoms. It may also help increase the number of blood cells.

Hydroxycarbamide is the most commonly used chemotherapy drug to treat MF. It is taken as a capsule or tablet. It can cause side effects, but these are generally mild. Side effects can include being more at risk of getting an infection, having a reduced number of red blood cells (anaemia), diarrhoea or constipation.

There may be a very small risk of leukaemia developing if hydroxycarbamide is used for a long time. Your doctor or specialist nurse can give you more information about this. Chemotherapy is not suitable for everyone with MF. It temporarily affects the way the bone marrow works and may reduce the level of blood cells, so if you have chemotherapy you'll be monitored very closely. Sometimes a smaller dose of chemotherapy is given to lower the risk of serious side effects. Your doctor or nurse will explain the possible side effects of any chemotherapy they recommend for you.

Chemotherapy may affect fertility. People taking it are advised not to get pregnant or father a child, as there may be a risk of harming the developing baby. Contraception should be used while taking the drug and also for a few months afterwards.

Targeted (biological) therapies

Targeted therapies (sometimes called biological therapies) can be used to stimulate the immune system, control the growth of cancer cells or to overcome side effects of treatment. They work by targeting how cancer cells work and grow.


Thalidomide is a type of targeted therapy used to treat MF. It can be given on its own or in combination with steroid tablets.  Thalidomide is taken as a tablet. The side effects can include feeling tired or sleepy, constipation and numbness or tingling of the hands and feet. If you feel sleepy, it’s important not to drive.

Thalidomide can cause birth defects, so it should not be given to pregnant women. People taking thalidomide who are sexually active must use a barrier form of contraception.

JAK inhibitors

JAK inhibitors, such as ruxolitinib (Jakavi®), are a new type of treatment. They work by blocking (inhibiting) the faulty JAK2 gene. Ruxolitinib is used for some people with an enlarged spleen or symptoms related to myelofibrosis.

Interferon alpha

Interferon is a natural substance made by the body. It can also be made as a medicine. It slows down the production of blood cells, including platelets. Interferon is given as an injection under the skin. Possible side effects include flu-like symptoms, headaches, dizziness, mood swings and tiredness.

Other drugs


This is a drug that may be given to help improve anaemia (low number of red blood cells).


Steroids may sometimes be used to treat low levels of red blood cells.


Erythropoietin is another treatment that may help to increase the levels of red blood cells in some people. It is given as an injection.

Removing the spleen (splenectomy)

If your spleen is enlarged and causing symptoms, your specialist may suggest that you have an operation to remove it.

There can be advantages and disadvantages to having this operation. Your specialist will discuss these with you before you make a decision.


If it isn’t possible to remove the spleen, it may be possible to shrink it using radiotherapy. Radiotherapy is the use of high-energy rays to destroy cancer cells, while doing as little harm as possible to the healthy cells. Radiotherapy can help improve symptoms such as pain and a high platelet count. But this improvement may only last for a few months.

Radiotherapy can cause temporary side effects, such as tiredness and skin irritation, although generally these are mild.

Stem cell transplant (from a donor)

Rarely, a stem cell transplant is used to treat people with myelofibrosis. You have high doses of chemotherapy, and sometimes radiotherapy. The stem cells that have been destroyed by the treatment are then replaced. The replacement stem cells are from a donor, who can be a brother, sister or an unrelated donor who is a match for you.

Some people may have less intense doses of chemotherapy to weaken their immune system enough to allow the donor stem cells to grow in their bone marrow. This is called reduced intensity conditioning (sometimes called a mini transplant).

Your doctor or nurse will explain your treatment and answer any questions that you have.

Clinical trials

There are also some newer treatments available, which may be used to help to control MF.

You may be invited to join a clinical trial looking at new ways of treating MF. You can talk about this with your haematology doctor.


You will need to have regular check-ups and blood tests. If you have any problems, or notice any new symptoms in between these appointments, let your nurse or doctor know as soon as possible.

Your feelings

You may have many different emotions including anger and resentment, guilt, anxiety and fear. These are all normal reactions, and are part of the process many people go through in trying to come to terms with their condition.

Everyone has their own way of coping with difficult situations. Some people find it helpful to talk to family or friends, while others prefer to seek help from people outside their situation. Some people prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is there if you need it. Our cancer support specialists can give you information about counselling in your area.

Usegful organisations

MPN Voice

MPN Voice is a support network for people with MPNs (myeloproliferative neoplasms), providing information and support. 

Leukaemia CARE

Leukaemia CARE is a national group promoting the welfare of people with leukaemia and other blood disorders. It has many regional support groups.

References and thanks

This page has been compiled using information from a number of reliable sources, including the electronic Medicines Compendium (eMC). If you’d like further information on the sources we use, please feel free to contact us.

This information was reviewed by a medical professional. Thank you to all of the people affected by cancer who reviewed what you're reading and have helped our information to develop.

You could help us too when you join our Cancer Voices Network – find out more.

Back to Other blood cancers

Myelodysplatic syndromes (MDS)

Myelodysplatic syndromes (MDS) are a group of conditions that affect the bone marrow. Sometimes, MDS can develop into acute leukaemia.