Essential thrombocythaemia (ET)

Essential thrombocythaemia (ET) is a rare condition which affects the bone marrow – the spongy material found in bones. Bone marrow is where our blood cells are made. In ET, too many platelets are made. Platelets help the blood to clot.

ET usually affects people over 50. It doesn’t always cause symptoms and may be found after a blood test is taken for other reasons.

Your doctor may suggest particular blood tests to diagnose ET. These can find gene changes which lead to ET. You may also have a bone marrow test. This is when a sample of bone marrow cells is taken from your back or hip bone, to be looked at by a doctor.

Treatment for ET aims to reduce the risk of complications. You may have chemotherapy (anti-cancer drugs) to reduce the number of platelets. Other treatments for ET include:

  • aspirin
  • interferon alpha
  • anagrelide
  • radioactive phosphorus (32P).

You will have regular blood tests and check-ups. You should let your doctor know if you notice any other symptoms.

The bone marrow

To understand ET, it helps to know a little about the 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 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.

The bone marrow makes millions of blood cells every day. When the cells are mature they are released into the blood stream. In myeloproliferative neoplasms (MPNs), bone marrow makes too many of one or more types of blood cells.

Myeloproliferative neoplasms (MPNs)

MPNs affect how the bone marrow works. The main types of MPN are:

  • essential thrombocythaemia
  • polycythaemia vera
  • myelofibrosis.

Some people with essential thrombocythaemia develop myelofibrosis. This is a condition in which the bone marrow becomes scarred. Rarely, people with MPNs develop leukaemia.

What is essential thrombocythaemia (ET)?

ET is a rare condition affecting the bone marrow. It happens when too many platelets are made. This means the number of platelets in the bloodstream becomes higher than normal.

ET can affect people at any age, including children, but it is most common in people over 50. It usually develops very slowly and for most people doesn't affect their normal life span.

Signs and symptoms of essential thrombocythaemia

Having too many platelets in the blood does not always cause symptoms. Some people are diagnosed with ET after they have a blood test for other reasons. Possible symptoms of ET include:

  • headaches
  • dizziness
  • redness, swelling or pain in the hands or feet due to reduced blood flow
  • tiredness
  • skin itching.

Sometimes symptoms develop due to complications of ET, such as a blood clot caused by too many platelets in the blood. Less commonly, people may have bleeding or bruising because the platelets in their blood don't work properly.

Blood clots

Symptoms can occur because a blood clot (thrombosis) has formed in a vein in the body. Clotting problems are more common in people over 60 and in people who have had a blood clot before. People who have conditions such as high blood pressure or diabetes are also more likely to have clotting problems.

Symptoms of a blood clot depend on where it is in the body. These are some common sites where a clot may form:

  • Veins of the leg – causing pain, swelling, heat and redness, usually in the calf. This is called deep vein thrombosis or DVT.
  • The brain – this may cause mild symptoms such as headaches, blurred vision, or dizziness. Blood clots in the brain may also cause a stroke or mini stroke (also called a transient ischaemic attack or a TIA). Symptoms may include weakness, numbness or pins and needles, or difficulties with speech or swallowing.
  • The heart – a blood clot in the heart may cause chest pain and, in severe cases, can result in a heart attack.
  • The lungs – a blood clot in a lung may cause breathlessness and chest pain. This is known as a pulmonary embolism or a PE.

Bleeding or bruising

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

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

Diagnosing essential thrombocythaemia

ET is usually diagnosed by a specialist in blood disorders (haematologist). The diagnosis may be suspected after a routine blood test called a full blood count (FBC). This test counts the number of red blood cells, white blood cells and platelets. In ET, there will be a high platelet count.

Other conditions can cause an increase in platelet count, such as an infection, arthritis, chronic bleeding or a lack of iron in the blood (anaemia). Your doctor will need to rule these out before a diagnosis of ET can be made.

Tests and investigations that may be done to confirm a diagnosis of ET are:

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 ET. 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 blood test

This blood test checks for a change (mutation) in a gene called JAK2. This gene helps control how many blood cells are made. About half of all people with ET have a mutation in the JAK2 gene.

CALR blood test

People who do not have a mutation in JAK2 might be checked for a mutation 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 marrow (biopsy) to be checked. The sample is usually taken from the back of your hip bone (pelvis). You’ll 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 into a syringe. This is called a bone marrow aspirate.

After this, the doctor will take a small core 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 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 sore for a few days after the test. You can take mild painkillers to help with this.

Treatment for essential thrombocythaemia

Treatment for ET aims is to reduce the risk of complications, particularly blood clots. Your doctor will check your condition with regular blood tests.

If treatment is successful, the outlook for someone with ET is very similar to someone of the same age who does not have it.


If you have a low risk of complications, you may be treated with aspirin. Aspirin can help prevent clots because it affects the way platelets stick together. This doesn’t affect the platelet count, but can help lower the risk of blood clots. Side effects of aspirin include an increased risk of bleeding and ulcers in the stomach.

If you need to take a painkiller while you are taking aspirin, ask your doctor for advice. Some types of painkillers, such as ibuprofen, may not be suitable.

Treatment to reduce platelet numbers (cytoreductive therapy)

If you are at high risk of complications, you will usually need treatment to reduce the numbers of platelets in your blood. This is called cytoreductive therapy. Different types of drugs can be used. Your doctor or specialist nurse will discuss treatment with you.


Chemotherapy is the use of anti-cancer drugs to destroy cancer cells. For ET, it is given to reduce the number of platelets.

Hydroxycarbamide is the most commonly used chemotherapy drug to treat ET. It is taken as a capsule or tablet. It can cause side effects, but generally these are mild. Side effects can include:

  • lowered resistance to infection
  • a reduced number of red blood cells (anaemia)
  • diarrhoea
  • constipation.

There may be a very small risk of leukaemia developing if hydroxycarbamide is used for a long time. Patients under the age of 40 with ET are usually given other drugs instead.

The chemotherapy drug busulfan may sometimes be used. Busulfan is given as a tablet. It can cause similar side effects to hydroxycarbamide. There is a risk of leukaemia developing if busulfan is used for a long time.

Chemotherapy may affect fertility. People taking it are advised not to get pregnant or father a child, as it can harm a developing baby. It's important to use effective contraception during and for a few months after chemotherapy.

Interferon alpha

Interferon alpha is a natural substance made by the body. It can also be made as a medicine (Intron A®, Roferon-A®). It slows down the production of blood cells, including platelets. It is used most often to treat ET in younger people (under 40), but it can be used at any age.

Interferon is given as an injection under the skin. Your doctor will explain how often you will have it. Possible side effects include flu-like symptoms, headaches, dizziness, mood swings and tiredness.


Anagrelide is usually given when other treatments have already been tried. It's taken as a capsule. Side effects can include headaches and palpitations (a fast heartbeat). Some research studies suggest it may increase the risk of developing myelofibrosis.

It doesn't seem to affect fertility, but anagrelide should never be taken during pregnancy or if you are thinking of getting pregnant. It's important to use contraception when taking anagrelide.

Radioactive phosphorus (32P)

Radioactive phosphorus may be used to treat ET when other treatments have not worked or are unsuitable. It is given as an injection into a vein. It irradiates the bone marrow and can lower the number of platelets being made. The effects of a single injection can last from months to years.

Long-term treatment with radioactive phosphorus can cause an increased risk of leukaemia.

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

Clinical trials

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

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

Living with essential thrombocythaemia

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

As well as the treatments and check-ups recommended by your haematologist, you may want to look at ways of staying healthy. Following a healthy diet, drinking plenty of fluids, staying active and not smoking are good for your general health. This may also help reduce the risk of complications such as blood clots. If you have high blood pressure (hypertension), keeping your blood pressure under control can also help. Your doctor or specialist nurse can give you advice about this.

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. You may also want to contact some support organisations:

  • MPN Voice is a support network for people with MPNs (myeloproliferative neoplasms) providing information and support.
  • Leukaemia CARE is a national group promoting the welfare of people with leukaemia and other blood disorders. It has regional support groups in many counties.

References and thanks

This page has been compiled using information from a number of reliable sources. 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.

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Back to Other blood cancers

Myelofibrosis (MF)

Myelofibrosis (MF) is a type of bone marrow disease. Rarely, MF leads to leukemia.

Myelodysplatic syndromes (MDS)

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