Thrombocythaemia | Cancer Research UK
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What essential thrombocythaemia is

Essential thrombocythaemia is pronounced essential throm-bo-sigh-thee-me-a. It is also called ET for short. It is one of a group of conditions called myeloproliferative disorders, or neoplasms (MPN). These blood conditions cause an increase in the number of blood cells. There is a separate general question and answer explaining myeloproliferative neoplasms.

ET is a rare blood disorder that causes a high number of blood cells called platelets to form. These are blood cells involved in blood clotting. Thrombo means clotting and cythaemia relates to 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 well as platelets, the bone marrow makes

  • Red blood cells to carry oxygen around our bodies
  • White blood cells to fight infection

The diagram shows how the various different types of cells develop from a single blood stem cell.


So, in essential thrombocythaemia, the stem cells make too many platelets. The excess platelets may form blood clots and can collect in the spleen, making it become enlarged.

Treatment controls essential thrombocythaemia for most people for many years. But for some, ET can lead to other problems. Some people develop scarring of their bone marrow. This is called myelofibrosis. The risk of this happening increases over time. Between 3 and 10 out of every 100 people (3 to 10%) develop myelofibrosis within 10 years of their diagnosis with ET. And between 6 and 30 out of every 100 people (6 to 30%) develop it between 10 and 20 years after diagnosis. More rarely ET can develop into an acute myeloid leukaemia. Fewer than 5 in 100 people (5%) with ET develop AML.


Risks and causes

We don’t know exactly what causes ET. Researchers have found that around half of those (50%) with essential thrombocythaemia have a change in the JAK2 gene. The JAK2 gene makes a protein that controls how many blood cells are made by the stem cells. This gene change causes too much of this protein to be made and that causes the stem cells to make more platelets. We need more research to find out what causes the change in the JAK2 gene.



ET usually develops slowly and doesn’t cause symptoms at first. So some people find out they have it when they are having a blood test for something else. As the condition progresses it causes symptoms.

Most of the symptoms happen as a result of blood clots forming or because of bleeding problems. Bleeding problems are less common than clots, but can develop because the platelets are not fully mature and don’t work normally. Symptoms include

  • Headaches
  • Blurred vision
  • Hearing problems
  • Burning and tingling in hands and feet
  • Swelling on your left side caused by an enlarged spleen
  • Nosebleeds
  • Bruising
  • Bleeding gums
  • Vaginal bleeding when you are not due to have a period, or abnormally heavy periods

The symptoms of a blood clot depend on where it is in the body. They can form anywhere but most commonly develop in the deep veins in the leg, lung, brain or heart. Not everyone with ET will have these problems. People who are over 60 years old, have diabetes or heart disease, and are overweight are at higher risk. If you have any of the following symptoms contact your doctor immediately

  • Pain, redness and a feeling of hotness in the leg could be a clot in the leg
  • Breathlessness and chest pain could be a lung clot (pulmonary embolism)
  • Headache, dizziness and blurred vision could be a clot in the brain
  • Chest pain could be a clot in the heart, and in more serious cases can cause a heart attack

Tests to diagnose essential thrombocythaemia

The first test is a blood test. This is to check the number of platelets you have. A normal platelet count is between 150,000 and 440,000 per cubic millimetre of blood. You are more likely to see this written as 150 and 440 x 10 9/l.

If your platelet count is higher than this your doctor will repeat the test. If it is still high you will have more tests.

Another blood test is to check for changes in genes that help control the number of platelets made. About half of those with ET (50%) have a change in the JAK2 gene and just under 1 in 20 people (5%) have a change in the MPL gene.

Other tests you may have include



Treatment for ET aims to reduce the number of platelets. This helps to control your symptoms. The treatment you need will depend on your risk of developing blood clots. Doctors group people into 3 risk groups – high, intermediate and low. People who are at high risk tend to

  • Be over 60 years old
  • Have had blood clots before
  • Smoke
  • Have high blood pressure
  • Have a platelet count of over 1500 x 10 9/l
  • Have a JAK2 gene change

Treatment usually includes aspirin and chemotherapy.

People who are low risk are under 40 and have a lower platelet count. Treatment for low risk is usually low dose aspirin.

If you are at intermediate risk your treatment will depend on the symptoms you have and your general health.

Treatments include

Low dose aspirin

You take aspirin as a tablet. This can help to lower the number of platelets in the blood.


Chemotherapy uses cell killing (cytotoxic) drugs to destroy the extra platelets. The drugs work by disrupting the growth of cells and stopping them from dividing. The most common type of chemotherapy doctors use to treat ET is hydroxycarbamide. It is a tablet. There may be a small increase in risk of developing a leukaemia if you take them for a long time.

Another type of chemotherapy you may have is busulfan. We know from research that it increases the risk of developing leukaemia if you take it for long periods of time. So you take it for a while and then stop for a period of time before starting again.


Anagrelide reduces the number of platelets. Doctors use it to treat ET when hydroxycarbamide is no longer working. Or you may have the two drugs together. Anagrelide does cause side effects that some people find difficult to cope with. These include breathlessness and tiredness from anaemia, a racing heart, headache and feeling sick. It can also cause more serious heart problems.


Interferon is a type of biological therapy and helps to boost the immune system. It can help to control the number of platelets. You usually have it as an injection under the skin, about 3 times a week. Side effects of interferon include flu like symptoms and tiredness. Pegylated interferon is being looked at in trials. It stays in the body for longer and so you usually only have this injection once a week.

Radioactive phosphorus

Radioactive phosphorus is a type of radiotherapy that helps to stop the bone marrow producing too many platelets. You may have this if you are older and have advanced disease. It isn’t a common treatment because research suggests it may increase the risk of developing leukaemia. There is more information about radioactive phosphorus therapy in the radiotherapy section.



Researchers are looking into new types of treatment to stop the JAK2 gene signalling to stem cells to make blood cells. These are called JAK2 inhibitors. This research is at an early stage but looks promising. It will be sometime before we know how well JAK2 inhibitors work.

Researchers are also looking into how myeloproliferative disorders develop. Some of this research is suggesting that it may be better to group them depending on whether they are JAK2 positive or negative rather than whether they are ET, myelofibrosis or polycythaemia vera. We need more research to find out the best way to group them and what the best treatment is.


Coping with essential thrombocythaemia

Coping with a rare condition can be difficult both practically and emotionally. Being well informed about your condition and possible treatments can make it easier to make decisions and cope with what happens.

It can also help to talk to people with the same thing. But it can be hard to find someone with a rare condition. Check out Cancer Chat – Cancer Research UK’s discussion forum. It is a place to share experiences, stories and information with other people who know what you are going through.

There are also a number of organisations that offer help and support

MPD Voice
They offer information and support to people with myeloproliferative disorders.

Leukaemia Care
They offer information and support to people with leukaemia and related blood conditions. They have a 24 hour care line and an online support service.

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Updated: 22 February 2014