Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Essential Thrombocythemia ?
    ### Response:
    Key Points
                    - Essential thrombocythemia is a disease in which too many platelets are made in the bone marrow.    - Patients with essential thrombocythemia may have no signs or symptoms.    - Certain factors affect prognosis (chance of recovery) and treatment options for essential thrombocythemia.
    