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About myelofibrosis

Read about the symptoms of myelofibrosis and how it is diagnosed.

What myelofibrosis is

Myelofibrosis (MF) is one of a group of blood conditions called myeloproliferative disorders or neoplasms.

It is pronounced my-eh-lo-fy-bro-sis. Myelo means bone marrow and fibrosis relates to the development of fibrous or scar tissue. The scar tissue builds up inside your bone marrow and blood cells can't develop properly. 

People who have no history of problems with their bone marrow can get MF. This is called primary myelofibrosis (PMF) or chronic idiopathic myelofibrosis.

Secondary myelofibrosis is where the condition develops in people who have other bone marrow disorders such as polycythaemia vera or thrombocythaemia. 

The bone marrow and blood cells

The bone marrow is the soft inner part of our bones that makes blood cells. All blood cells start from the same type of cell, called a stem cell. The stem cell makes immature blood cells.

The immature cells go through various stages of development before they become fully developed blood cells and are released into the blood as:

  • 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 various types of cell develop from a single blood stem cell.

Diagram showing how blood cells are made

How myelofibrosis affects the blood cells

In people with MF scar tissue builds up inside the bone marrow and blood cells are not made properly. The bone marrow gradually produces fewer blood cells. 

As the number of new blood cells fall in the bone marrow, the liver and spleen try to make more blood cells. But they're not as good at making them as the bone marrow, so you might develop anaemia (not enough red blood cells in your blood). 

The spleen can also become enlarged, as instead of releasing the red blood cells into the blood it keeps hold of them. This might cause discomfort in your tummy, or make you feel full when you eat.

As myelofibrosis develops, the bone marrow also makes fewer white blood cells and platelets. 

Myelofibrosis and cancer

How myelofibrosis develops in people can vary. Treatment can control myelofibrosis for many people for some time.

Some people develop more serious problems, such as heart disease and infections that might be difficult to control.

Between 1 and 2 out of every 10 people diagnosed with myelofibrosis (10 to 20%) go on to develop a type of leukaemia called acute myeloid leukaemia (AML). In this situation, your doctor would talk to you about starting treatment for AML.

Risks and causes

Researchers have found that about half of people who have myelofibrosis (50%) have a change in a gene called JAK2. The JAK2 gene makes a protein that controls how many blood cells the stem cells make. Another gene change is the CALR gene, around 25% of people will have this gene change. 

When the JAK2 or CALR gene becomes mutated, your bone marrow may not function correctly and scar tissue can build up in your bone marrow.

About a third of those with myelofibrosis have a history of essential thrombocythaemia or polycythaemia vera.


Myelofibrosis usually develops slowly and doesn’t cause symptoms at first. About a third of people who are diagnosed find out about it when having a blood test for something else.

As the condition progresses it causes symptoms, including: 

  • tiredness and shortness of breath – due to low numbers of red blood cells
  • bleeding and bruising easily – due to low numbers of platelets
  • pain and discomfort in the abdomen due to enlarged spleen and liver
  • bone pain
  • gout
  • loss of appetite and weight loss
  • fever and night sweats

Tests to diagnose myelofibrosis

You have a blood test to check your blood cell count. Most people are anaemic but some people have a normal or increased haemoglobin. Haemoglobin is a protein in red blood cells that carries oxygen around the body.

Many people have higher than normal white blood cell count and platelets at diagnosis but these usually drop as the disease progresses.

You usually have a bone marrow biopsy and an ultrasound of your spleen. The spleen is on the left hand side of your tummy (abdomen).

If these tests suggest you have myelofibrosis, you then have another blood test to look for gene changes.


Your treatment depends on a number of factors including your blood count at diagnosis, the symptoms you have and the number of immature cells you have in your blood. 

Treatment can control myelofibrosis for some time, although this varies from person to person.

Last reviewed: 
06 Sep 2017
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  • Myelodysplastic syndromes: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow up 

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