Chronic Myeloproliferative Neoplasms Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Essential Thrombocythemia
There is no staging system for this disease.
Untreated essential thrombocythemia means that a patient is newly diagnosed and has had no prior treatment except supportive care.
Controversy is considerable regarding whether asymptomatic patients with essential thrombocythemia require treatment. In a case-controlled, observational study of 65 low-risk patients (<60 years of age, platelet count <1,500 × 109 /L, and no history of thrombosis or hemorrhage) with a median follow-up of 4.1 years, the thrombotic risk of 1.91 cases per 100 patient years and hemorrhagic risk of 1.12 cases per 100 patient years was not increased any more than in the normal controls.
- A randomized trial of patients with essential thrombocythemia and a high risk of thrombosis compared treatment with hydroxyurea titrated to attain a platelet count below 600,000/mm3 with a control group that received no therapy. Hydroxyurea was found to be effective in preventing thrombotic episodes (4% vs. 24%).[Level of evidence: 1iiDiv] A retrospective analysis of this trial found that antiplatelet drugs had no significant influence on the outcome. Resistance to hydroxyurea is defined as a platelet count of greater than 600,000/mcL after 3 months of at least 2 g per day of hydroxyurea or a platelet count greater than 400,000/µL and a white blood count of less than 2,500/µL or a hemoglobin less than 10 g/dL at any dose of hydroxyurea.
- A prospective, randomized trial in the United Kingdom (UK) of 809 patients compared hydroxyurea plus aspirin with anagrelide plus aspirin. Although the platelet-lowering effect was equivalent, the anagrelide group had significantly more thrombotic and hemorrhagic events (hazard ratio [HR], 1.57; P = .03) and more myelofibrosis (HR, 2.92; P = .01). No differences were seen for subsequent myelodysplasia or acute leukemia in this trial.[Level of evidence: 1iiD]
- Another prospective, randomized trial also compared hydroxyurea and anagrelide in 259 previously untreated and high-risk patients. In this central European trial, the diagnosis of essential thrombocythemia was made by the WHO recommendations, not by the Polycythemia Vera Study Group criteria as in the UK study. This means that patients with leukocytosis and a diagnosis of early prefibrotic myelofibrosis (both groups with much higher rates of thrombosis) were excluded from the central European trial. In this analysis, there were no differences in outcome for thrombotic or hemorrhagic events.[Level of evidence: 1iiD]