Clinical parameters for determining when and when not to treat essential thrombocythemia.

Essential thrombocythemia (ET) is a myeloproliferative disorder that occurs primarily in middle-aged adults. ET is relatively benign compared with some of the other myeloproliferative disorders (MPDs), but there is still a high rate of morbidity and quality of life can be affected, especially by thrombotic and hemorrhagic complications. Two thirds of ET patients are symptomatic, but therapies are not benign. While alkylating agents, radioactive phosphorous, and hydroxyurea (HU) all have a leukemogenic risk, their use in high-risk and elderly patients may still be warranted in some circumstances. Use of nonmutagenic agents such as anagrelide, interferon-alpha (IFN), or low-dose aspirin has become an attractive alternative. However, the risks and benefits of treatment versus nontreatment should be based on clinical data and must be determined on an individual basis.