ConditionBlood & immune system
Essential Thrombocythemia (ET)
Essential thrombocythemia (ET) is a rare, slow-growing blood cancer in which the bone marrow makes too many platelets, the cells that help blood clot. Many people have no symptoms and are diagnosed after a routine blood test shows a platelet count above 450,000 per microliter. ET raises the risk of blood clots, and at very high counts, bleeding. Treatment depends on risk: low-dose aspirin for many, plus medicines that lower platelets for higher-risk people. Most live a normal or near-normal lifespan.
Also called: ET, essential thrombocytosis, primary thrombocythemia, idiopathic thrombocythemia
At a glance
- What it is
- A myeloproliferative neoplasm with overproduction of platelets by the bone marrow.
- Who gets it
- Usually diagnosed around age 50 to 60, more often in women; can occur in younger adults.
- Gene changes
- JAK2 (about half), CALR (about a quarter), MPL (a few percent); some have none of these.
- Main risks
- Arterial and venous clots; bleeding with extremely high counts; rare progression to myelofibrosis or leukemia.
- Treatment
- Low-dose aspirin; hydroxyurea, interferon or anagrelide for high-risk patients.
When to get help
Call 911 or go to the ER
- Sudden weakness, numbness, facial droop, slurred speech or vision loss: call 911 or your local emergency number (possible stroke)
- Chest pain, sudden shortness of breath, or a swollen painful leg with breathlessness
- Severe abdominal pain with a swollen belly (possible clot in abdominal veins)
- Heavy bleeding that will not stop, vomiting blood or black stools
See a doctor within a day or two
- New burning pain, redness or warmth in the hands or feet (erythromelalgia)
- Brief episodes of vision change, numbness or speech difficulty that resolved
- Pregnancy in someone with ET
Book a routine appointment
- A platelet count above 450,000 per microliter on more than one test
- Headaches, dizziness or tingling with a known high platelet count
What essential thrombocythemia is
ET is one of the myeloproliferative neoplasms (MPNs), a group of chronic blood cancers that also includes polycythemia vera and myelofibrosis. A gene change in a blood stem cell causes the marrow to overproduce megakaryocytes, the cells that make platelets. Platelet counts can reach 600,000 to over 1,000,000 per microliter, compared with a normal range of about 150,000 to 450,000.
ET is uncommon, with about 1 to 2.5 new cases per 100,000 people each year. It is not inherited in most cases, though MPNs are somewhat more common in relatives.
The term primary thrombocythemia is used almost interchangeably; see primary thrombocythemia for how a high platelet count is investigated and how ET is distinguished from reactive causes.
Symptoms
About half of people have no symptoms at diagnosis. When symptoms occur, they are mostly due to small-vessel circulation problems or clots:
- headaches and migraine-like episodes
- dizziness or lightheadedness
- visual disturbances, such as flashing lights or brief blurring
- tingling or numbness in the hands and feet
- erythromelalgia: burning pain, redness and warmth in the hands or feet, typically relieved by aspirin
- fatigue
- an enlarged spleen in some people, causing fullness in the upper left abdomen
Clots
- arterial: stroke, transient ischemic attack, heart attack
- venous: deep vein thrombosis, pulmonary embolism, and clots in unusual places such as the abdominal veins
Bleeding
Paradoxically, very high platelet counts (often above 1,000,000 to 1,500,000) can cause bleeding, such as nosebleeds, gum bleeding, easy bruising or gut bleeding, because an important clotting protein (von Willebrand factor) is used up.
Diagnosis
Diagnosis follows the World Health Organization criteria, which require:
- a sustained platelet count of 450,000 per microliter or higher
- a bone marrow biopsy showing increased large, mature megakaryocytes without features of other MPNs
- ruling out other myeloid cancers such as chronic myeloid leukemia (BCR-ABL negative) and polycythemia vera
- a JAK2, CALR or MPL mutation, or another clonal marker, or no evidence of reactive thrombocytosis
Tests
- complete blood count and blood smear
- iron studies, inflammatory markers and other tests to exclude reactive causes (iron deficiency, infection, inflammation, cancer, spleen removal)
- JAK2, CALR and MPL mutation testing, and BCR-ABL testing
- bone marrow biopsy
Risk categories
Treatment decisions are guided by risk scores such as the revised IPSET-thrombosis model:
| Risk group | Typical features |
|---|---|
| Very low | Age 60 or under, no previous clot, no JAK2 mutation |
| Low | Age 60 or under, no previous clot, JAK2 mutation |
| Intermediate | Over 60, no previous clot, no JAK2 mutation |
| High | Previous clot, or over 60 with JAK2 mutation |
Cardiovascular risk factors (smoking, high blood pressure, diabetes, high cholesterol) also raise clot risk and must be managed.
Treatment
Low-dose aspirin
Recommended for most people with JAK2 mutations or circulation symptoms, to lower clot risk and relieve erythromelalgia. It may be avoided when the platelet count is extremely high (because of bleeding risk) or in some very low-risk patients.
Platelet-lowering (cytoreductive) therapy
For high-risk patients:
- hydroxyurea: a pill that reduces platelet production; first-line for most
- pegylated interferon alfa: an injection, often preferred in younger people and during pregnancy
- anagrelide: a pill that specifically lowers platelets, used when hydroxyurea is not suitable
Other measures
- stop smoking and control blood pressure, cholesterol and diabetes
- anticoagulants after venous clots
- careful planning before surgery and during pregnancy with a hematologist
Outlook
Life expectancy for most people with ET, especially younger and lower-risk patients, is near normal. Over 10 to 20 years, a minority progress to myelofibrosis, and a small number (a few percent) transform to acute myeloid leukemia. Regular blood count checks track the disease.
Frequently asked questions
What are the symptoms of essential thrombocythemia?
Many people have no symptoms. When present, symptoms include headaches, dizziness, visual disturbances, tingling or burning in the hands and feet, fatigue, and sometimes clots or abnormal bleeding. Erythromelalgia, burning red hands or feet, is characteristic.
Is essential thrombocythemia a cancer?
Yes, it is classified as a chronic blood cancer (a myeloproliferative neoplasm), but it usually progresses very slowly. Most people live a normal or near-normal lifespan, and many need only aspirin and monitoring.
What causes essential thrombocythemia?
ET is caused by an acquired gene change in a blood stem cell, most often in JAK2, CALR or MPL. These mutations make the bone marrow overproduce platelets. It is not usually inherited and is not caused by lifestyle.
What is the life expectancy with essential thrombocythemia?
For most people, especially those diagnosed younger and at lower risk, life expectancy is close to normal. Risk of clots is the main concern, and a small number of people progress to myelofibrosis or acute leukemia over many years.
What is the treatment for essential thrombocythemia?
Many people take low-dose aspirin to lower clot risk. Those at high risk, for example over 60 with a JAK2 mutation or a previous clot, also take medicines that lower platelet counts, such as hydroxyurea, interferon or anagrelide.
Sources
This guide was written from current patient and clinical guidance, including:
- National Comprehensive Cancer Network (NCCN): Myeloproliferative Neoplasms Guideline
- American Society of Hematology: Myeloproliferative Neoplasms
- MPN Research Foundation: Essential Thrombocythemia
- World Health Organization: Classification of Haematolymphoid Tumours (5th edition)
- MedlinePlus: Primary thrombocythemia