Essential Thrombocythemia

Essential Thrombocythemia (ET) is a type of chronic myeloproliferative neoplasm caused by abnormal blood forming cells that overproduce a blood cell called platelets (aka thrombocytes). Like CML, ET is also thought to be caused by mutations in blood forming stem cells (aka hematopoietic stem cell, HSC). Everyone is born with a few tens of thousands of HSCs that are the source for all of the blood cells people make during their life. In ET, mutations in one of two genes, JAK2 and CALR, are found in the blood cells of most patients. These mutations cause the HSCs to yield too many platelets in relationship to the other blood cell types. Whereas a normal platelet count can range from 150,000 to 450,000 platelets per microliter of blood, someone with ET has more than 450,000 platelets per microliter of blood. ET is more common in people over the age of 50, however, young people can also develop it. It is also more common in women for reasons that are not understood. It is an uncommon disease and it is not clear why some people get ET while most others do not. ET does not generally run in families although very rarely, this does happen. Since ET is an uncommon disease, it is important to be evaluated and treated at a specialized center by physicians who are experts in the field.

Most people with ET will require some therapy. For patients with a higher risk of problems from their ET, treatments that lower platelet counts and blood thinners may be necessary. Those with a mild form of ET may not need any treatment. Aspirin is generally recommended to reduce the risk of blood clots. Sometimes, the first indication that someone has ET is the development of an abnormal blood clot. Clots can develop anywhere in the body, either in veins or arteries. Conversely, some patients with ET and very high platelet counts are at risk for abnormal bleeding. Most of the therapy for ET is directed at minimizing the risk of abnormal blood clots and abnormal bleeding. Although this is relatively uncommon, ET can progress to more serious blood cancers such as myelofibrosis or acute leukemia.

There is no cure for ET, short of a hematopoietic stem cell transplant, but there are treatments available and with appropriate treatment, lifespan is usually normal. Specific treatment for ET is dependent upon risk of blood-clotting or bleeding episodes. It is possible that if a patient is younger than 60 years old and has not had signs or symptoms, only periodic medical checkups may be necessary. Medication may be prescribed if the patient is older than 60 and/or has a history of blood clots. Many treatments are available for those patients such as Hydrea, Agrylin, or Pegasys, plus low-dose aspirin to reduce platelet count.  

Treatment Overview

The goals of treatment for ET are aimed at reducing the risk of the most common serious medical problems faced by patients with ET: abnormal blood clots (link to thrombosis complication); and abnormal bleeding (link to bleeding complication). There are no universally accepted standard guidelines for therapy but there are several recommendations that are commonly used.

Richard T. Silver MD Myeloproliferative Neoplasms Center 525 East 70th St., Starr Pavillion, 3rd Floor New York, NY 10021