Essential thrombocythemia is an example of a myeloproliferative neoplasm. These are blood cancers that happen when your body produces too many blood cells. from Cleveland Clinic
from JohnsHopkins
Myeloproliferative neoplasms (MPNs) are a group of blood cancers in which the bone marrow produces too many blood cells. When this happens, patients are at risk for blood clotting or bleeding, bone marrow scarring and enlargement of the organs. Most patients affected are in their 60s or older. There are no known cures for most MPNs, although stem cell transplants can help people with myelofibrosis. Still, many patients can experience few or no symptoms for long periods of time, and people with these cancers can live for a long time with proper monitoring and treatment.