What is essential thrombocythaemia (ET)?

Essential thrombocythaemia (ET) is a type of blood cancer that affects the bone marrow. Bone marrow is where blood cells are made. In ET, the body makes too many platelets.

Platelets are cells in the blood that cause it to stick together and form clots to stop bleeding. Having too many platelets increases the risk of having unwanted blood clots. If platelets in the blood do not work properly, it increases the risk of bleeding.

ET usually develops very slowly. For most people, having ET does not shorten their life. ET is more common in people aged over 60, but it can affect people at any age.

To understand ET and its treatment, it can help to know more about the blood and bone marrow.

Symptoms of essential thrombocythaemia (ET)

Having too many platelets in the blood does not always cause symptoms. Some people are diagnosed with ET when they have a blood test for another reason.

Possible symptoms of ET include:

  • persistent headaches
  • dizziness or ringing in the ears (tinnitus)
  • numbness or tingling in the hands and feet
  • burning pain, changes in feeling, or redness in the hands or feet
  • cold or blue fingers or toes
  • tiredness
  • difficulty concentrating
  • changes in vision
  • itchy skin
  • bone pain.

Possible complications of ET

Some people also develop symptoms because of the complications of ET.

Blood clots

Some people with ET have a higher risk of developing a blood clot. Symptoms of a blood clot include:

  • throbbing pain, redness or swelling in a leg or an arm
  • suddenly feeling breathless or coughing
  • sharp chest pain, which may be worse when you cough or take a deep breath.

If you have any of these symptoms, contact the hospital straight away. If you cannot speak to your doctor, call the NHS urgent advice number on 111.

A blood clot is serious, but it can be treated with drugs that thin the blood (anti-coagulants). Your doctor or nurse can give you more information. You may be given drugs to help prevent a clot.

Blood clots can also cause heart attacks and strokes. If you think you may be having a heart attack or stroke, call 999 for an ambulance or go straight to A&E (emergency department).

Bleeding or bruising

Sometimes, ET can cause abnormal bleeding or bruising. But this is less common than a blood clot. Bleeding is most likely to happen if your platelets are not working properly or your platelet level is very high (over 1,500). Any bleeding might be heavier than normal and take longer to stop.

Symptoms may include:

  • nosebleeds
  • bleeding gums
  • heavy periods
  • blood in your pee (urine) or poo (stools)
  • very dark poo
  • blood in your vomit (sick) – this can be a bright red liquid, or look like brown or black coffee granules
  • tiny red or purple spots on your skin that may look like a rash.

Tell your doctor if you notice any signs of abnormal bleeding or bruising.

If you think you see blood in your sick or poo, or if you have dark poo, or if any bleeding is heavy or will not stop, contact a doctor urgently. If you cannot speak to a doctor, call 999 for an ambulance or go straight to A&E.


When the body tries to break down (get rid of) more blood cells than usual, it can cause a painful condition called gout. Gout affects the joints. It causes pain, heat, redness and swelling. It usually only affects the big toe joint. But it can affect other joints, especially in the hands and feet.

Gout is caused by uric acid building up in the blood. Uric acid is produced when lots of cells are broken down. The uric acid forms crystals that get into the joint and cause the symptoms.

Usually, the kidneys can clear uric acid from the blood and pass it out of the body in the pee. But sometimes, they cannot cope with large amounts.

Your doctor can check the level of uric acid with a blood test. Depending on the result, they may give you a tablet called allopurinol to help prevent gout.

Enlarged spleen

The spleen is an organ that sits on the left side of the tummy (abdomen), just under the ribs. It is usually about the size of a fist.

The spleen
Image: The spleen

The spleen:

  • helps fight infection
  • stores and breaks down blood cells.

ET can cause the spleen to grow bigger than normal (enlarged), but this is usually mild. Symptoms of an enlarged spleen include discomfort on the left side of the tummy and feeling full quickly when eating.

Having an enlarged spleen can cause problems. It may:

  • keep blood cells in the spleen instead of releasing them into the blood
  • destroy blood cells.

Both these changes can reduce the number of blood cells in the blood.

Myelofibrosis (MF)

A very small number of people with ET may develop a more serious condition called myelofibrosis (MF). Myelofibrosis causes scarring of the bone marrow. This scarring can cause changes in blood cell counts, an enlarged spleen and other symptoms.

Acute myeloid leukaemia (AML)

Rarely, ET can cause a rare type of blood cancer called acute myeloid leukaemia (AML).

Diagnosis of essential thrombocythaemia (ET)

There is no specific test for diagnosing ET. Your GP might suspect you have ET if you have a raised number of platelets in your blood over a period of time. This can be measured in a blood test called a full blood count (FBC).

But ET is not the only cause of a raised number of platelets. Other causes include:

If your doctor thinks you may have ET, they will refer you to the hospital to see a specialist blood doctor called a haematologist.

At your hospital appointment, you may also meet a clinical nurse specialist. They may be your key worker. This means they are your main contact for information and support.

Your haematologist will decide whether you need further tests. This can include more blood tests and a bone marrow biopsy.

  • Genetic tests

    Genes carry the instructions that cells in the body need to work properly. There are genes that control how many blood cells are made in the bone marrow. Genes can develop changes over time. Genetic changes do not always cause problems, but they can cause conditions such as ET.

    Some genetic changes that develop over time are known to cause ET. You may have blood tests to look for changes in the following genes:

    • JAK2 – around 60 out of 100 people with ET (60%) will have this change
    • CALR – around 25 out of 100 people with ET (25%) will have this change
    • MPL – around 5 out of 100 people with ET (5%) will have this change.

    Some people with ET do not have any of these genetic changes. This is called triple negative ET. ET can be more difficult to diagnose when a genetic change cannot be found.

  • Bone marrow biopsy

    Your doctor may want to take a sample of bone marrow to look at under a microscope. This is called a bone marrow biopsy. Doctors usually remove the sample from the back of the hip bone (pelvis).

    The sample is sent to a laboratory to be checked for abnormal cells.

  • Ultrasound scan

    Sometimes your spleen gets bigger when you have ET. Your doctor may be able to feel this by examining your tummy. Or you may have an ultrasound scan.

Waiting for test results can be a difficult time. It may help to talk to family members, friends or your clinical nurse specialist.

Treatment for essential thrombocythaemia (ET)

Before treatment, a team of health professionals work together to plan the treatment they feel is best for you. This team is called a multi-disciplinary team (MDT).

The MDT look at the risk of you developing problems from ET. They also look at your test results and general health. They will describe the ET as low, intermediate (medium) or high risk based on:

  • your age
  • your symptoms
  • your medical conditions
  • the number of platelets in your blood
  • whether genetic tests show the gene changes linked to ET
  • whether you have had blood clots.

Treatment for ET is usually given to prevent complications such as blood clots. This is called supportive treatment. You have regular blood tests to check for changes in your condition.

Not everyone with ET needs treatment. Your haematologist will talk to you about your situation.

You may be offered treatment as part of a clinical trial.

Preventing blood clots

If you have ET, you have a higher risk of blood clots. Blood clots can sometimes cause a serious condition by blocking blood flow:

  • in the lungs – this is called a pulmonary embolism (PE)
  • in an arm or a leg – this is called a deep vein thrombosis (DVT)
  • to the heart – this may cause a heart attack
  • to an area of the brain – this may cause a stroke.

Your haematologist or clinical nurse specialist will give you advice and information about how to reduce your risk. This may include information about the following:

Managing other conditions

Your doctor can help you manage any other conditions you have that may also increase your risk of blood clots, such as:

  • diabetes
  • high blood pressure
  • high cholesterol.

Lifestyle changes

Your doctors and nurses will give you advice about any lifestyle changes you can make to help reduce your risk. They usually advise you to:


Most people with ET are treated with aspirin tablets. Aspirin affects the way platelets stick together and helps prevent blood clots. Drugs that prevent clots are called anti-platelet drugs or blood thinners. Aspirin does not affect the number of platelets in the blood.

One of the side effects of aspirin is an increased risk of bleeding and ulcers in the stomach.

If you are taking aspirin, ask your doctor for advice about painkillers. Certain types of painkillers, such as ibuprofen, may not be suitable for you while you are taking aspirin.

If you cannot take aspirin because of medical conditions such as a stomach ulcer, you may be given another anti-platelet drug called clopidogrel instead.

Reducing platelets

If you have a high risk of blood clots, you usually have treatment to reduce the number of platelets in your blood. This is called cytoreductive therapy. Your haematologist or clinical nurse specialist will talk to you about your treatment.

Cytoreductive therapies include the following:


You may have chemotherapy to reduce the number of platelets in the blood.

Hydroxycarbamide (HC) is the most commonly used chemotherapy drug to treat ET. You take it as a capsule or tablet. It can cause side effects, but these are usually mild.

Taking HC for a long time can increase the risk of getting a skin cancer. It is important that you protect your skin from the sun. You also need to check for any changes in your skin during and after treatment with HC. Your haematologist or clinical nurse specialist can tell you more about this.

Another chemotherapy drug called busulfan is sometimes used. You have this as a tablet. The side effects are like the side effects of HC. If you take busulfan for a long time, it may slightly increase your risk of developing leukaemia.

Interferon alpha

Interferon is a protein made naturally by the body. It can also be made as a drug (interferon alpha) and given as an injection under the skin (subcutaneous). It slows down how quickly the bone marrow makes blood cells, including platelets.


Anagrelide is a drug usually given after you have already had other treatments to reduce your platelet levels. You take it as a capsule.

Side effects can include headaches and changes to your heart rate and rhythm. You may have tests to check your heart before you start taking anagrelide. Some research suggests that anagrelide may increase the risk of getting myelofibrosis.

Radioactive phosphorus (32P)

Rarely, a treatment called radioactive phosphorus may be used. You have it as an injection into a vein. It gives a dose of radiation to the bone marrow and reduces the number of platelets being made. You usually only have this treatment when other treatments are not suitable or have not worked.

The effects of a single treatment with radioactive phosphorous can last from months to years. Having long-term treatment with radioactive phosphorus increases the risk of leukaemia.

Pregnancy, fertility and essential thrombocythaemia (ET)

If you are planning to get pregnant or to make someone pregnant in the next few months, talk to your doctor first.

Chemotherapy and some other treatments may affect the development of an unborn baby. Doctors usually advise against getting pregnant or making someone pregnant during these treatments and for a few months after. It is important to use effective contraception.

Chemotherapy may affect fertility. If this is a concern for you, talk to your doctor before starting treatment.

If you are planning to get pregnant, ET can increase the risk of complications during pregnancy. But with risk-reducing treatments and careful monitoring during pregnancy, most babies are born healthy. Your haematologist and obstetrician (doctor who specialises in pregnancy) will work together to give you the best care during your pregnancy.

During pregnancy, your doctor usually advises you to take aspirin daily. This reduces the risk of complications from blood clots for both you and the baby. If you need other treatment to reduce your risk of complications, your doctor may advise having interferon alpha.

Living with essential thrombocythaemia (ET)

If you have ET, you need regular check-ups and blood tests. If you are worried or notice any new symptoms between appointments, tell your haematologist or clinical nurse specialist as soon as possible.

Making lifestyle changes to reduce your risk of complications can sometimes be challenging. You may find it easier to make changes as part of a group or with help from others. If you find it hard to make changes, tell your GP, practice nurse or haematology team. There is lots of support available to help you live a healthier lifestyle.

Your feelings

Everyone has their own way of dealing with the different feelings they experience. You may find it helpful to talk about things with family members, friends, or your specialist doctor or nurse.

Macmillan is also here to support you. If you would like to talk, you can:

The organisations below also offer information and support: 

  • MPN Voice

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

  • Leukaemia Care

    Leukaemia Care is a national blood cancer support charity for people with leukaemia and other blood disorders. It has regional support groups.

  • Blood Cancer UK 

    Blood Cancer UK is a blood cancer research charity that provides information and support on any type of blood cancer.

About our information

  • References

    Below is a sample of the sources used in our essential thrombocythaemia (ET) information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    Pan-London Haemato-Oncology Clinical Guidelines Acute Leukaemias and Myeloid Neoplasms Part 4: Myeloproliferative Neoplasms. January 2020. Available from www.rmpartners.nhs.uk/wp-content/uploads/2020/01/Pan-London-MPN-Guidelines-Jan-2020.pdf (accessed July 2022).

    Barbui T, Thiele J, Ferrari A, Vannucchi A and Tefferi A. The new WHO classification for essential thrombocythemia calls for revision of available evidences. Blood Cancer Journal, volume 10, Article number: 22 (2020). 

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Anne Parker, Consultant Haematologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 March 2023
Next review: 01 March 2026
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.