Essential thrombocythemia (ET) is a type of myeloproliferative neoplasm (MPN), a kind of blood cancer that is closely related to leukemia, lymphoma, and myeloma. Previously called myeloproliferative disorders, MPNs are caused by the proliferation (excessive growing and dividing) of blood cells in the bone marrow. Different types of MPN are caused by an overabundance of different types of blood cells — in case of ET, the condition is caused by too many platelets. MPNs such as essential thrombocythemia are chronic and progressive; although they usually progress slowly, the condition worsens over time.
Essential thrombocythemia, sometimes called hemorrhagic thrombocythemia, is a rare chronic MPN. ET cancer cells come from a type of cell in the bone marrow called megakaryocytes, which form platelets. Platelets are blood cells primarily responsible for clotting. Essential thrombocythemia results in the body making too many platelets, a condition called thrombocytosis or a high platelet count. Having too many platelets leads to abnormal blood clotting and blockages in blood vessels. There may also be excessive bleeding.
Essential thrombocythemia is classified as a “classic” type of myeloproliferative neoplasm, a group that also includes polycythemia vera and primary myelofibrosis. The three classic MPNs are also known as Philadelphia chromosome-negative MPNs, because they do not have a specific genetic abnormality seen in certain other types of MPNs.
ET is more common in women, according to Cleveland Clinic, and is usually diagnosed later in life, between ages 50 and 70. ET also occurs in younger adults and, rarely, in children.
Essential thrombocythemia is a type of cancer, and cancers are caused by cells that develop genetic mutations. Normally, when cells develop mutations, they are destroyed by the immune system. Sometimes, though, cells continue to grow and divide uncontrollably, becoming cancer cells.
Specific genetic mutations are often associated with different types of ET. Most cases of ET have a mutation in the Janus kinase 2 (JAK2) gene. This mutation is called JAK2V617F. Other mutations seen in ET occur in the calreticulin (or CALR) and myeloproliferative leukemia (or MPL) genes. Some cases of ET do not have any of these three mutations, in which case the ET is called triple-negative ET.
The specific cause of these mutations and precisely how they cause the development of ET is unclear. In general, genetic mutations that cause cancer can be passed down from your parents or acquired over the course of your lifetime by normal aging, exposure to radiation, exposure to certain chemicals, or infection with certain viruses. Essential thrombocythemia is not an inherited disease, but the cause is unknown.
Read more about the causes of MPN.
Essential thrombocythemia is usually discovered before any symptoms develop. When symptoms of ET develop, they are usually a result of thrombosis (the formation of blood clots inside blood vessels). When blood clots form inside veins and arteries they can block blood flow to parts of the body. Blood clots can occur in small blood vessels, such as capillaries, or large blood vessels, such as the femoral veins in the legs. Clots in large blood vessels can lead to serious complications such as heart attack, stroke, transient ischemic attack (also called a ministroke), deep vein thrombosis, and pulmonary embolism.
Generalized symptoms seen in ET as a result of abnormal platelet activity include:
Abnormal bleeding can cause signs and symptoms, such as:
Learn about the symptoms of MPN.
Essential thrombocythemia is usually discovered during routine blood tests, before any symptoms develop. A complete blood count (CBC) showing an unusually high number of platelets is usually the first sign of disease. Further testing using bone marrow biopsy and tests for specific genetic mutations may be used to diagnose ET and rule out other conditions.
Read more about MPN diagnosis.
Essential thrombocythemia is not a curable form of cancer, but it is very treatable. The main goals of treatment are to reduce platelet counts and prevent blood clots.
The choice of treatment depends on what symptoms a person has and their risk category. Risk of thrombosis is assessed using a person’s platelet counts, age, history of thrombosis or bleeding, history of smoking or high blood pressure, and presence of the JAK2 mutation in the cancer cells. People aged 60 and older and those with a history of thrombosis are at an increased risk of blood clots.
Asymptomatic people with essential thrombocythemia may not require immediate treatment. A “watch and wait” approach, also called active surveillance, involves close follow-up and periodic blood tests. If symptoms develop or the disease progresses, then a doctor may consider treatment.
Several drugs are commonly used to treat essential thrombocythemia:
Enrollment in clinical trials is another option for treatment. Clinical trials can test new drugs, new combinations of drugs, or new uses for existing drugs to find better treatments for ET. One drug being tested to treat ET is ruxolitinib, a JAK-inhibitor used to treat other forms of classic myeloproliferative neoplasms.
Read more about MPN treatments.
The outlook for essential thrombocythemia varies based on a person’s risk factors and how advanced their particular disease is. Preventing blood clots and bleeding is the key to avoiding serious complications from ET. People at low risk for blood clots may have a normal life expectancy with ET, while people at high risk have a median survival of 8 to 16 years after diagnosis, depending on their individual risk factors.
In about 5 percent of cases, ET can lead to scarring inside the bone marrow (myelofibrosis). Very rarely, ET can progress to become acute myeloid leukemia.
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