Intermittent melphalan in the treatment of essential thrombocytosis with haemorrhage or thrombosis

[Treatment of essential thrombocythemia]

PURPOSE

Essential thrombocythemia (ET) is a myeloproliferative syndrome that rises many therapeutic problems. This affection is rarely life threatening, but hemorrhagic and thrombotic complications must be prevented when possible. The rarity of these complications makes difficult the assessment of treatment efficiency. Few randomised clinical trials were done, and treatment often rests on retrospective studies. The potential toxicity of treatments, their leukemogenicity in particular, rises a decisional problem for young patients. We propose to review available data in order to propose the most rational treatment for each patient.

CURRENT KNOWLEDGE AND KEY POINTS

After numerous years when we only disposed of retrospective studies, non-randomised prospective studies or isolated case-reports, two randomised trials allows us to more precisely define ET treatment. The first trial proved the efficiency of the hydroxyurea-aspirin association in the prevention of thrombotic events in high-risk patients. The second trial signalled to our attention the increased risk of bleeding of the association anagrelide-aspirin, with also the possibility of increased appearance of myelofibrosis.

FUTURE PROSPECTS AND PROJECTS

New perspectives in the treatment of ET will require to get more insights in the role of hydroxyurea and anagrelide in particular by longer follow-up. But not less important is a better definition of the thrombosis risks (who has to be treated?) and also of the diagnostic groups since ET can, in some particular cases, be misdiagnosed with polycythemia vera or idiopathic myelofibrosis.

Essential thrombocythemia (ET): moving from palliation to cure

Essential thrombocythemia (ET) is a clonal hematopoietic stem cell myeloproliferative disorder characterized by megakaryocytic hyperplasia and persistent thrombocytosis. The clinical presentation and evolution of ET are heterogeneous. This review highlights the current treatment options in the management of ET, including hydroxyurea, anagrelide and both regular and pegylated interferons. Anagrelide, while very effective at controlling counts and symptoms in most patients, may not consistently reduce the bone marrow megakaryocyte mass. Interferon is very effective and not associated with leukemogenesis, but has not been proven to restore polyclonal hematopoiesis and has significant dose-related adverse events. Pegylated interferon represents a significant improvement over the unmodified interferon preparations. Novel therapeutic options directed towards eradication of the malignant ET clone are required.

Treatment strategies in essential thrombocythemia. A critical appraisal of various experiences in different centers

The therapeutic strategy in patients with Essential Thrombocythemia (ET) is a difficult balance between the prevention of bleeding and thrombotic complications and the risks of drug side effects and toxicity. Major bleeding is rare and seem to be related to higher platelet counts: therefore, a platelet count over 1500 x 10(9)/L is generally regarded as an indication for cytoreduction. Thrombotic complications include microvascular occlusive symptoms, which are reversible with low-dose aspirin, and large vessels thrombosis. The risk of major thrombosis is higher in ET patients aged more than 60 ys. and with previous occlusive event. In this high-risk group, the non-alkylating agent hydroxyurea (HU) significantly reduces the rate of vascular complications and has emerged as the treatment of choice. However, the long-term risk/benefit of HU remains disputed because its leukemogenic potential has not been ruled out. This holds also for other myelosuppressive agents, such as busulphan and pipobroman. Other drugs of particular interest for young patients include recombinant alpha-interferon (IFN) and Anagrelide. Both of them are effective in lowering platelet count, but their efficacy in reducing clinical complications remains to be demonstrated. However, both IFN and Anagrelide have shown to have frequent and clinically important side effects. Thus, further clinical studies are required to establish their role in the strategy of ET patient treatment.

Remission may continue after termination of rIFN alpha-2b treatment for essential thrombocythemia

Essential thrombocythemia, a myeloproliferative disorder of clonal origin, is often associated with various clinical manifestations resulting from thromboembolic or hemorrhagic complications. The long-established successful method of treatment with cytotoxic agents or radioactive phosphorus has recently been superseded by interferon alpha. We treated 14 symptomatic patients with 5 x 10(6) IU recombinant interferon alpha-2b s.c. daily. 12/14 pts responded within 14-75 days. When platelet counts decreased to below 450 g/l the frequency of administration was reduced stepwise. 7 patients remained in CR during this reduction phase and treatment was stopped in 5 pts after 12-32 months. Until now, 3 of them are still in continuous good PR without any drug therapy and free of symptoms for 3+, 19+ and 36+ months. Continuous response during maintenance was associated with age, initial platelet count and time required to reduce platelet counts to less than 450 g/l.

Recombinant interferon-alpha, but not interferon-gamma is effective therapy for essential thrombocythemia

Recombinant interferon-gamma with a starting dose of 0.5 mg 3x/week subcutaneously, was administered to 6 patients with essential thrombocythemia (median platelet count 1172 X 10(9)/l, range 602-1564). Four of the patients had received alkylating agents previously. Hematological remission, defined as a decrease in platelet counts to less than or equal to 350 X 10(9)/l, was observed in none of these patients. Subsequently 4 of these 6 patients, supplemented by 2 others were treated with interferon-alpha 2c at a dose of 5 X 10(6) U daily subcutaneously. Five patients showed hematological remission. In case of hematological remission the interferon-alpha doses was reduced to 5 X an thereafter to 3 X weekly 5 X 10(6) U. During an observation period ranging from 12-41 weeks platelet counts remained normal in all patients. Side-effects were mild and consisted of fever, myalgias, malaise and itching occurring mainly during the first month of treatment. No dose adaptation was required. The patients treated previously with interferon-gamma experienced the side effects from this drug less tolerably than those from the alpha-compound. These observations suggest that recombinant interferon-alpha may be an effective drug in treating essential thrombocythemia resulting in a sustained response.

The treatment of essential thrombocythaemia with radioactive phosphorus

The major complications of essential thrombocythaemia include haemorrhage and thrombosis, events which are related to the level of the abnormal platelet count. We report here on the use of radioactive phosphorus (32P) in eight patients with essential thrombocythaemia. Two patients required multiple injections of 32P to control platelet count, and there was no reduction in the rate of fall of platelets with each injection. Three patients required chemotherapy for persistent thrombocythaemia despite multiple doses of 32P. No clinical or haematological characteristics could be identified for those patients whose disease was difficult to control. Radioactive phosphorus is a safe and effective method to control platelet counts in patients with essential thrombocythaemia.

Bleeding and coagulation disorders in the elderly

Ageing does not bring with it any major changes in the coagulation or fibrinolytic proteins or platelets. It does bring a greater burden of disease, with less reserves, and so when haemorrhage occurs in the elderly it has more serious consequences. The cause of a bleeding diathesis can usually be determined after a careful history, and examination of the patient followed by simple tests--the platelet count, blood film, bleeding time, prothrombin time, partial thromboplastin time, thrombin time, fibrin degradation products and the euglobulin clot lysis time. Other confirmatory tests, assays and inhibitor titres, will seal the diagnosis. Treatment is mainly directed at removing the underlying cause, if possible, and remedying the defect, with platelet transfusion, fresh frozen plasma or factor concentrates. These treatments will not be effective where there is an inhibitor or antibody present; steroids, splenectomy (for ITP), plasma exchange or immunosuppression are needed. Two major advances have occurred in the early 1980s. One has been the introduction of high-dose intravenous immunoglobulin in the management of ITP, although worries remain about thrombotic events in elderly patients. The other is the spreading use of DDAVP, originally introduced for von Willebrand's disease and mild haemophilia, and now finding a role in uraemia and with cardiopulmonary bypass. Drugs are a significant and potentially preventable cause of bleeding in the elderly. The most frequent problems arise with anticoagulants. The risk of interactions increase with the number of other medications which are prescribed.