What is Essential Thrombocythemia?

Essential thrombocythemia (ET), also known as essential thrombocytosis, is a rare blood condition in which the body makes too many platelets. This overproduction happens because of genetic changes in bone marrow stem cells, leading to a group of diseases called myeloproliferative neoplasms (MPNs). ET is often slow-growing (indolent), but it can cause serious complications like blood clots, bleeding, and sometimes transform into other blood cancers like myelofibrosis or acute myeloid leukemia. However, with modern treatments, most individuals with the disorder have a normal lifespan.

Symptoms can include fatigue, headaches, dizziness, tingling in hands or feet, or no symptoms at all. Most patients find out they have ET after a routine blood test shows a high platelet count (over 450,000 per microliter).

Types of Essential Thrombocythemia

There are no specific types of essential thrombocythemia. ET is classified based on the presence or absence of a specific mutation in the Janus kinase 2 (JAK2) gene. This mutation is found in other myeloproliferative disorders, suggesting that there is a common pathway in the development of all myeloproliferative disorders. The presence or absence of this mutation may have implications for the treatment and prognosis of the disease.

• JAK2 mutation (about 55% of cases): Often linked to a higher risk of blood clots.
• CALR mutation (about 20–25%): Tends to occur in younger people and has a lower risk of clotting.
• MPL mutation (3–5%): May increase the chance of disease progression.
• Triple-negative ET: No JAK2, CALR, or MPL mutation; more common in children.

Why Do People Get Essential Thrombocythemia?

The cause of essential thrombocythemia is unknown. However, most patients with this condition have mutations in the JAK2, CALR, or MPL genes. These mutations develop over a person's lifetime, are present only in certain cells, and are not inherited. They lead to the overproduction of platelets, contributing to the signs and symptoms of ET.

In many cases, people with ET have no identifiable risk factors. However there are factors that may increase the risk of developing ET, for example:

• Genetic mutations (especially JAK2, CALR, MPL)
• Age: Most people are diagnosed between ages 50–60
• Sex: Women are affected more often than men
• Family history: Rare inherited cases exist

Who Gets Essential Thrombocythemia?

According to the National Cancer Institute, there will be an estimated 38 to 57 new cases per 100,000 people of essential thrombocythemia in 2023. 

Is Essential Thrombocythemia Considered Cancer?

Yes. Essential thrombocythemia is classified as a type of blood cancer, specifically a myeloproliferative neoplasm. It involves abnormal growth of blood cells in the bone marrow. While many people with ET live long lives, it is a chronic condition that requires ongoing care to prevent serious complications.

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