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Myelofibrosis (MF)

We're here for you if you want to talk

0808 2080 888

[email protected]

What is myelofibrosis (MF)?

MF is a rare type of blood cancer that causes scar tissue to form in your bone marrow (the spongy material inside some of your bones). As this builds up, blood cells can no longer develop properly inside your bone marrow.

In MF, your bone marrow is overactive and then develops scar tissue (known as fibrosis). The scar tissue builds up inside your bone marrow (the spongy material inside some of your bones) and blood cells can’t develop properly inside it.

When blood cell production is reduced in the bone marrow, it starts to take place in the liver and spleen instead. As the liver and spleen aren’t as good at producing blood cells, people with MF may develop anaemia (not enough red blood cells in your blood).

The spleen may also become enlarged, as it ‘holds on’ to red blood cells instead of releasing them into the blood.

People who have no history of problems with their bone marrow can get MF. This is known as primary myelofibrosis (PMF). Secondary MF is where the condition develops as a result of other blood cancers such as polycythaemia vera (PV) and essential thrombocythaemia (ET).

MF, PV and ET are all types of blood cancer known as myeloproliferative neoplasms (MPN).

What causes MF?

The underlying causes of MF are still not fully understood, but you may hear your doctor talking about a genetic fault in your JAK2, CALR or MPL gene, which they think is involved in causing MF. Around 65% of patients with MF will have the JAK2 gene. 25% of people will have the CALR gene and up to 8% will have the MPL one.

All cells in your body contain a set of instructions which tell the cell what to do and when to do it, stored inside the cells in structures called chromosomes. The chromosomes are made up of a chemical known as DNA.

The DNA is arranged in sections called genes. There are 23 pairs of chromosomes in each cell in your body. When cells divide to form new cells, normally the chromosomes stay the same in each new cell.

A small genetic change to DNA can cause a genetic fault. These changes can be caused by exposure to hazardous chemicals or copying mistakes when a cell was dividing. When the JAK2, CALR or MPL gene becomes mutated, your bone marrow may not function correctly and scar tissue can build up in your bone marrow.

It’s important to note that these genetic faults happen during a person’s lifetime. As you’re not born with these faults, you can’t pass these on to your children.

The presence of one of these genes in your blood might lead to doctors diagnosing you with MPN. However, we‘re learning about these faulty genes, and their impact on treatment options and prognosis (forecasting the future of the disease), all the time. If you’d like to know more about those genes, your consultant will be happy to talk to you about them.

As well as the presence of certain genetic faults, there are other factors which might lead to a higher risk of getting MF.


People who get MF are usually between 50 and 70 years old. The condition is rare in children, but can occur at any age.


Men and women have an equal chance of developing MF.

Previous diagnosis of an MPN

A previous diagnosis of PV or ET may increase the risk of getting MF, in which case it’s known as secondary MF.

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