Disease Overview
Treatment Overview
Current Clinical Trials

Note: Some citations in the text of this section are followed by a level of evidence. The PDQ editorial boards use a formal ranking system to help the reader judge the strength of evidence linked to the reported results of a therapeutic strategy. (Refer to the PDQ summary on Levels of Evidence ¹ for more information.)

Essential thrombocythemia is characterized by:

• A platelet count of more than 600,000/mm³.



• Profound megakaryocytic hyperplasia in the bone marrow.



• Absence of increased red blood cell mass (polycythemia), myelodysplasia, or chronic myelogenous leukemia (absence of BCR/ABL fusion gene).



• Absence of a disorder associated with reactive thrombocytosis, such as severe iron deficiency, cancer, surgery, or infection (normal ferritin).



• JAK2 mutation in the presence of a high platelet count (>450,000/mm³).[1]

Although the karyotype is usually normal, patients older than 60 years or those with a prior thrombotic episode have as much as a 25% chance of developing cerebral, cardiac, or peripheral arterial thromboses and, less often, a chance of developing a pulmonary embolism or deep venous thrombosis.[2] Similar to the other myeloproliferative syndromes, conversion to acute leukemia is found in a small percentage of patients (<10%) with long-term follow-up.

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. 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%).[2][Level of evidence: 1iiDiv] A retrospective analysis of this trial found that antiplatelet drugs had no significant influence on the outcome.

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 over the normal controls.[3] A prospective randomized trial of 809 patients compared hydroxyurea ± aspirin versus anagrelide ± aspirin.[4] 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 myelodysplasia or acute leukemia.[5][Level of evidence: 1iiA] Many clinicians use hydroxyurea or platelet apheresis prior to elective surgery to reduce the platelet count and to prevent postoperative thromboembolism. No prospective or randomized trials document the value of this approach.

Treatment options:

1. No treatment, unless complications develop, if patients are asymptomatic, younger than 60 years, and have a platelet count of less than 1,500 × 10⁹/L.



2. Hydroxyurea.[2]



3. Interferon-alpha.[6,7]



4. Anagrelide.[5,8]

Check for U.S. clinical trials from NCI's PDQ Cancer Clinical Trials Registry that are now accepting patients with essential thrombocythemia ². The list of clinical trials can be further narrowed by location, drug, intervention, and other criteria.

General information about clinical trials is also available from the NCI Web site ³.

References

1. Campbell PJ, Green AR: The myeloproliferative disorders. N Engl J Med 355 (23): 2452-66, 2006.  [PUBMED Abstract]
   
   
2. Cortelazzo S, Finazzi G, Ruggeri M, et al.: Hydroxyurea for patients with essential thrombocythemia and a high risk of thrombosis. N Engl J Med 332 (17): 1132-6, 1995.  [PUBMED Abstract]
   
   
3. Ruggeri M, Finazzi G, Tosetto A, et al.: No treatment for low-risk thrombocythaemia: results from a prospective study. Br J Haematol 103 (3): 772-7, 1998.  [PUBMED Abstract]
   
   
4. Harrison CN, Campbell PJ, Buck G, et al.: Hydroxyurea compared with anagrelide in high-risk essential thrombocythemia. N Engl J Med 353 (1): 33-45, 2005.  [PUBMED Abstract]
   
   
5. Green A, Campbell P, Buck G: The Medical Research Council PT1 trial in essential thrombocythemia. [Abstract] Blood 104 (11): A-6, 2004. 
   
   
6. Sacchi S: The role of alpha-interferon in essential thrombocythaemia, polycythaemia vera and myelofibrosis with myeloid metaplasia (MMM): a concise update. Leuk Lymphoma 19 (1-2): 13-20, 1995.  [PUBMED Abstract]
   
   
7. Gilbert HS: Long term treatment of myeloproliferative disease with interferon-alpha-2b: feasibility and efficacy. Cancer 83 (6): 1205-13, 1998.  [PUBMED Abstract]
   
   
8. Anagrelide, a therapy for thrombocythemic states: experience in 577 patients. Anagrelide Study Group. Am J Med 92 (1): 69-76, 1992.  [PUBMED Abstract]
   
   

Glossary Terms

Randomized, controlled, nonblinded clinical trial with total mortality as an endpoint. See Levels of Evidence for Adult and Pediatric Cancer Treatment Studies (PDQ®) for more information.

Randomized, controlled, nonblinded clinical trial with tumor response rate as an endpoint. See Levels of Evidence for Adult and Pediatric Cancer Treatment Studies (PDQ®) for more information.