The effect of interferon alpha on myeloproliferation and vascular complications in polycythemia vera

Clinical outcomes of interferon therapy for polycythemia vera and essential thrombocythemia: a systematic review and meta-analysis

Interferon therapy has been used in clinical practice for more than three decades to treat polycythemia vera (PV) and essential thrombocythemia (ET). However, there has been no systematic investigation of its expected outcomes and potential risks. We performed a systematic review and single-arm meta-analysis to assess the clinical outcomes (hematological response, molecular response, vascular events, hematological transformation, and adverse events) after interferon therapy for patients with PV and ET. A systematic search identified 37 reports, including data from 1794 patients that were published before March 2021. The pooled overall hematological response (OHR) rate was 86%, with better OHR rates observed in studies using long-acting interferon (p < 0.001) and studies with younger patients (p = 0.038). The pooled overall molecular response rate was 48%, and inter-study heterogeneity was also related to patient age (p = 0.009). The overall incidence was 0.42/100 person-years for thrombosis, 0.01/100 person-years for hemorrhage, 0.21/100 person-years for myelofibrotic transformation, and 0.08/100 person-years for leukemic transformation. Compared with hydroxyurea, interferon produced a non-inferior hematological response and a superior molecular response. In conclusion, interferon therapy provided high rates of hematological and molecular response for patients with PV and ET and was associated with a favorable prognosis.

Interferon alpha therapy in essential thrombocythemia and polycythemia vera-a systematic review and meta-analysis

Data on the efficacy and safety of interferon (IFN)-α for the treatment of essential thrombocythemia (ET) and polycythemia vera (PV) are inconsistent. We conducted a systematic review and meta-analysis and searched MEDLINE and EMBASE via Ovid, Scopus, COCHRANE registry of clinical trials, and Web of Science from inception through 03/2019 for studies of pegylated IFN (peg-IFN) and non-pegylated IFN (non-peg-IFN) in PV and ET patients. Random-effects models were used to pool response rates for the primary outcome of overall response rate (ORR) defined as a composite of complete response, partial response, complete hematologic response (CHR) and partial hematologic response. Peg-IFN and non-peg-IFN were compared by meta-regression analyses. In total, 44 studies with 1359 patients (730 ET, 629 PV) were included. ORR were 80.6% (95% confidence interval: 76.6-84.1%, CHR: 59.0% [51.5%-66.1%]) and 76.7% (67.4-84.0%; CHR: 48.5% [37.8-59.4%]) for ET and PV patients, respectively. In meta-regression analyses results did not differ significantly for non-peg-IFN vs. peg-IFN. Annualized rates of thromboembolic complications and treatment discontinuation due to adverse events were low at 1.2% and 8.8% for ET and 0.5% and 6.5% for PV patients, respectively. Both peg-IFN and non-peg-IFN can be effective and safe long-term treatments for ET and PV.

Drug-Related Cutaneous Adverse Events in Philadelphia Chromosome-Negative Myeloproliferative Neoplasms: A Literature Review

Since myeloproliferative neoplasms (MPN) pose a significant risk for vascular and thrombotic complications, cytoreductive therapies, such as hydroxyurea (HU), interferon (IFN) inhibitors, and Janus kinase (JAK) inhibitors are recommended for patients at high risk. However, these agents also place patients at increased risk for drug-related cutaneous adverse events. Herein, we review the literature on skin toxicity related to the use of drugs for the treatment of MPN. Overall, the cytoreductive agents used for MPN are generally well tolerated and considered to be safe, except IFN, for which dropout rates as high as 25% have been reported. While IFN is known to give rise to flu syndrome, it rarely leads to hematological alterations. The most common hematological side effects of HU are mild and include granulocytopenia, anemia, and thrombocytopenia. The JAK inhibitor ruxolitinib has been associated with cytopenia and a higher incidence of viral infections, as well as increased risk for basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Based on the present analysis, it can be concluded that cutaneous toxicity is not a negligible complication of commonly used treatments for MPN. While further research is needed, patients on these agents, and especially those with a history of cutaneous malignancies, should undergo thorough skin examination before and during therapy. In addition, detailed history is critical since many patients who develop non-melanoma skin cancer have multiple preexisting risk factors for cutaneous carcinogenesis.

Ropeginterferon alfa-2b versus standard therapy for polycythaemia vera (PROUD-PV and CONTINUATION-PV): a randomised, non-inferiority, phase 3 trial and its extension study

BACKGROUND

The PROUD-PV and CONTINUATION-PV trials aimed to compare the novel monopegylated interferon ropeginterferon alfa-2b with hydroxyurea, the standard therapy for patients with polycythaemia vera, over 3 years of treatment.

METHODS

PROUD-PV and its extension study, CONTINUATION-PV, were phase 3, randomised, controlled, open-label, trials done in 48 clinics in Europe. Patients were eligible if 18 years or older with early stage polycythaemia vera (no history of cytoreductive treatment or less than 3 years of previous hydroxyurea treatment) diagnosed by WHO's 2008 criteria. Patients were randomly assigned 1:1 to ropeginterferon alfa-2b (subcutaneously every 2 weeks, starting at 100 μg) or hydroxyurea (orally starting at 500 mg/day). After 1 year, patients could opt to enter the extension part of the trial, CONTINUATION-PV. The primary endpoint in PROUD-PV was non-inferiority of ropeginterferon alfa-2b versus hydroxyurea regarding complete haematological response with normal spleen size (longitudinal diameter of ≤12 cm for women and ≤13 cm for men) at 12 months; in CONTINUATION-PV, the coprimary endpoints were complete haematological response with normalisation of spleen size and with improved disease burden (ie, splenomegaly, microvascular disturbances, pruritus, and headache). We present the final results of PROUD-PV and an interim analysis at 36 months of the CONTINUATION-PV study (per statistical analysis plan). Analyses for safety and efficacy were per-protocol. The trials were registered on EudraCT, 2012-005259-18 (PROUD-PV) and 2014-001357-17 (CONTINUATION-PV, which is ongoing).

FINDINGS

Patients were recruited from Sept 17, 2013 to March 13, 2015 with 306 enrolled. 257 patients were randomly assigned, 127 were treated in each group (three patients withdrew consent in the hydroxyurea group), and 171 rolled over to the CONTINUATION-PV trial. Median follow-up was 182·1 weeks (IQR 166·3-201·7) in the ropeginterferon alfa-2b and 164·5 weeks (144·4-169·3) in the standard therapy group. In PROUD-PV, 26 (21%) of 122 patients in the ropeginterferon alfa-2b group and 34 (28%) of 123 patients in the standard therapy group met the composite primary endpoint of complete haematological response with normal spleen size. In CONTINUATION-PV, complete haematological response with improved disease burden was met in 50 (53%) of 95 patients in the ropeginterferon alfa-2b group versus 28 (38%) of 74 patients in the hydroxyurea group, p=0·044 at 36 months. Complete haematological response without the spleen criterion in the ropeginterferon alfa-2b group versus standard therapy group were: 53 (43%) of 123 patients versus 57 (46%) of 125 patients, p=0·63 at 12 months (PROUD-PV), and 67 (71%) of 95 patients versus 38 (51%) of 74 patients, p=0·012 at 36 months (CONTINUATION-PV). The most frequently reported grade 3 and grade 4 treatment-related adverse events were increased γ-glutamyltransferase (seven [6%] of 127 patients) and increased alanine aminotransferase (four [3%] of 127 patients) in the ropeginterferon alfa-2b group, and leucopenia (six [5%] of 127 patients) and thrombocytopenia (five [4%] of 127 patients) in the standard therapy group. Treatment-related serious adverse events occurred in three (2%) of 127 patients in the ropeginterferon alfa-2b group and five (4%) of 127 patients in the hydroxyurea group. One treatment-related death was reported in the standard therapy group (acute leukaemia).

INTERPRETATION

In patients with early polycythaemia vera, who predominantly presented without splenomegaly, ropeginterferon alfa-2b was effective in inducing haematological responses; non-inferiority to hydroxyurea regarding haematological response and normal spleen size was not shown at 12 months. However, response to ropeginterferon alfa-2b continued to increase over time with improved responses compared with hydroxyurea at 36 months. Considering the high and durable haematological and molecular responses and its good tolerability, ropeginterferon alfa-2b offers a valuable and safe long-term treatment option with features distinct from hydroxyurea.

FUNDING

AOP Orphan Pharmaceuticals AG.

Second line therapies in polycythemia vera: What is the optimal strategy after hydroxyurea failure?

Cytoreductive therapies have traditionally been the standard treatment for older patients with polycythemia vera (PV) or those with a history of prior thrombosis. Hydroxyurea (HU) is the most frequently used cytoreductive agent in PV. However, approximately 24% of patients treated with HU will eventually develop resistance or intolerance and patients who fail HU have an increased risk of death, transformation to myelofibrosis or acute myeloid leukemia. Interferon-alpha has been used in younger PV patients and is capable of inducing a complete hematologic response and significant reductions, or even eradication, of JAK2 V617F mutation allele burdens in a small but notable subset of PV patients. The potential toxicities of interferon-alpha must be weighed against the disease control benefit in a case-by-case fashion. Recently JAK2 inhibitor, ruxolitinib, demonstrated significant improvement in controlling the hematocrit and splenomegaly versus best available therapy in patients with PV who failed or are intolerant to HU and currently is FDA-approved in this setting. In this review, we will discuss novel emerging therapies for PV with a special focus on the currently available and upcoming treatment options for patients who fail HU.

Where to Turn for Second-Line Cytoreduction After Hydroxyurea in Polycythemia Vera?

The goals of therapy in patients with polycythemia vera (PV) are to improve disease-related symptoms, prevent the incidence or recurrence of thrombosis, and possibly delay or prevent the transformation into myelofibrosis or acute myeloid leukemia (AML). Cytoreductive therapies have been used in older patients and those with a history of thrombosis to achieve these goals. Hydroxyurea (HU) remains the first-line cytoreductive choice; however, up to one in four patients treated with HU over time will develop resistance or intolerance to HU. More importantly, patients who fail HU have a 5.6-fold increase in mortality and a 6.8-fold increase risk of transformation to myelofibrosis or AML; therefore, alternative therapies are needed for these patients. Interferon-α has been used in PV and has shown significant activity in achieving hematologic responses and decreasing JAK2 V617F mutation allele burden. JAK inhibition has also been investigated and recently garnered regulatory approval for this indication. In this review, we will discuss the current treatment options that are available for patients after HU and the novel therapies that are currently under investigation.

IMPLICATIONS FOR PRACTICE

The outcomes of PV patients who fail or who are intolerant of hydroxyurea are poor. Although pegylated interferon can be considered in younger patients, currently, ruxolitinib is the only U.S. Food and Drug Administration-approved agent in this setting, representing a viable option, leading to hematocrit control and a reduction in spleen size and constitutional symptoms. Although a small number of patients will achieve a molecular response with continuous treatment, the implications of such response on the clinical outcomes are still unknown. Patients whose disease is not adequately controlled with ruxolitinib, or who lose their response, can be treated with low-dose busulfan or pipobroman; however, they should be encouraged to participate in trials with novel therapies.

Ropeginterferon alfa-2b, a novel IFNα-2b, induces high response rates with low toxicity in patients with polycythemia vera

In this prospective, open-label, multicenter phase 1/2 dose escalation study, we used a next-generation, mono-pegylated interferon (IFN) α-2b isoform, ropeginterferon alfa-2b. The unique feature of ropeginterferon alfa-2b is a longer elimination half-life, which allows administration every 2 weeks. We present data from 51 polycythemia vera patients. The main goal was to define the maximum tolerated dose and to assess safety and efficacy. A dose range of 50 to 540 µg was tested without the appearance of dose-limiting toxicities. All drug-related adverse events were known toxicities associated with IFN-α. The cumulative overall response rate was 90%, comprising complete response in 47% and partial response in 43% of patients; the best individual molecular response level was a complete response in 21% of patients and partial response in 47%. Notably, we did not observe any correlation between the dose level and the response rate or response duration, suggesting that already low levels of ropeginterferon alfa-2b are sufficient to induce significant hematologic and molecular responses. These data suggest promising efficacy and safety of ropeginterferon alfa-2b and support the development of the drug in a randomized phase 3 clinical trial. The study was disclosed at www.clinicaltrials.gov as #NCT01193699 before including the first patient.

Interferon-alpha therapy in bcr-abl-negative myeloproliferative neoplasms

Interferon (IFN) was the first cytokine discovered 50 years ago, with a wide range of biological properties, including immunomodulatory, proapoptotic and antiangiogenic activities, that rapidly raised interest in its therapeutic use in malignancies. IFN-receptor characterization was also pivotal in the discovery of the JAK/STAT signaling pathway. Among the large IFN family, mainly one of the type I IFN, IFN-alpha2, is used in therapy. Many clinical trials have shown remarkable efficacy of IFN-alpha in bcr-abl-negative myeloproliferative neoplasms (MPNs), especially polycythemia vera (PV), and essential thrombocythemia (ET). IFN-alpha induces about 80% of hematological responses in those diseases and is able to reduce splenomegaly, as well as relieve pruritus and other constitutional symptoms. Yet its use was limited by toxicity, leading to early treatment discontinuation in about 20% of the patients. However, its lack of leukemogenic potential and its possible use during pregnancy have already made IFN-alpha the drug of choice for younger MPN patients. In addition, several studies have shown a probably selective effect of IFN-alpha on PV and ET clones, as shown by cytogenetic remissions, reversions to polyclonal hematopoiesis, and more recently by induction of JAK2V617F complete molecular remissions in PV which may widen the indications of IFN-alpha in JAK2-mutated MPN.

A review of the therapeutic agents used in the management of polycythaemia vera

The acquired clonal disorder Polycythaemia Vera leads to increased erythropoiesis, myelopoiesis and megakaryopoeisis. These anomalies result in an increased incidence of thromboembolic events, transformation to acute leukaemia and myelofibrosis. Treatments which aim to reduce the event rate may increase anaemia but may also affect the rate of complications. This paper reviews the evidence for the treatments which have been used in the management of the disorders over a 50 plus year period. Assessment of this evidence and its limitations form the basis for the current suggested management plans.

The treatment of polycythaemia vera: an update in the JAK2 era

The clinical course of polycythaemia vera is marked by a high incidence of thrombotic complications, which represent the main cause of morbidity and mortality. Major predictors of vascular events are increasing age and previous thrombosis. Myelosuppressive drugs can reduce the rate of thrombosis, but there is concern that their use raises the risk of transformation into acute leukaemia. To tackle this dilemma, a risk-oriented management strategy is recommended. Low-risk patients should be treated with phlebotomy and low-dose aspirin. Cytotoxic therapy is indicated in high-risk patients, with the drug of choice being hydroxyurea because its leukaemogenicity is low. The recent discovery of JAK2 V617F mutation in the vast majority of polycythaemia vera patients opens new avenues for the treatment of this disease. Novel therapeutic options theoretically devoid of leukaemic risk, such as alpha-interferon and imatinib, affect JAK2 expression in some patients. Nevertheless, these drugs require further clinical experience and, for the time being, should be reserved for selected cases.

Evidence-based management of polycythemia vera

The clinical course of polycythemia vera is marked by significant thrombotic complications and a variable risk of the disease turning either into myeloid metaplasia with myelofibrosis or into acute myeloid leukemia. Cytoreductive treatment of blood hyperviscosity by phlebotomy or chemotherapy and antiplatelet therapy with low-dose aspirin have dramatically reduced the number of thrombotic complications and substantially improved survival. However, there is concern that certain myelosuppressive drugs accelerate the disease progression to acute leukemia. Thus, the objective of management is two-fold: first, to minimize the risk of thrombotic complications; second, to prevent progression to myelofibrotic or leukemic transformation. This chapter provides updated estimates of the risk of thrombosis and disease progression and evaluates the various randomized and observational studies in polycythemia vera, according to an evidence-based approach.

Platelets and Thrombosis in Myeloproliferative Diseases

The myeloproliferative disorders have been the “poor cousins” in the family of hematological malignancies for some time. Recently this field has advanced considerably with the description of a mutation in the JAK2 kinase detectable in the majority of patients and the publication of two landmark clinical trials—ECLAP and MRC PT1. But although both ECLAP and MRC PT1 inform clinical management and allude to the complexities of thrombosis we still lack fundamental knowledge, and our understanding of thrombosis in these conditions has not paralleled advances in the field of thrombosis and vascular biology. The predominant clinical complications of essential thrombocythemia and polycythemia vera are thrombotic and hemorrhagic; these significantly impact upon prognosis and quality of life. Here the current status of our knowledge is reviewed with specific emphasis upon the role of the platelet in the pathogenesis of thrombosis as well as the impact of recent data from ECLAP and MRC PT1.

Platelets and Thrombosis in Myeloproliferative Diseases

The myeloproliferative disorders have been the “poor cousins” in the family of hematological malignancies for some time. Recently this field has advanced considerably with the description of a mutation in the JAK2 kinase detectable in the majority of patients and the publication of two landmark clinical trials—ECLAP and MRC PT1. But although both ECLAP and MRC PT1 inform clinical management and allude to the complexities of thrombosis we still lack fundamental knowledge, and our understanding of thrombosis in these conditions has not paralleled advances in the field of thrombosis and vascular biology. The predominant clinical complications of essential thrombocythemia and polycythemia vera are thrombotic and hemorrhagic; these significantly impact upon prognosis and quality of life. Here the current status of our knowledge is reviewed with specific emphasis upon the role of the platelet in the pathogenesis of thrombosis as well as the impact of recent data from ECLAP and MRC PT1.

Anagrelide for thrombocytosis in myeloproliferative disorders: a prospective study to assess efficacy and adverse event profile

BACKGROUND

Although the platelet count does not correlate with the rate of thrombosis, there is evidence that a strict control of the platelet count decreases the incidence of thromboembolic complications in essential thrombocythemia. In the current study, the authors evaluated the efficacy and tolerability of anagrelide in thrombocytosis associated with myeloproliferative disorders.

METHODS

The study cohort comprised 97 patients (n = 69 females, n = 28 males) with a median age of 59 years (range, 21-80 years). Patients with essential thrombocythemia (n = 79) or with thrombocytosis due to polycythemia vera (n = 16) or to chronic idiopathic myelofibrosis (n = 2) were enrolled in the multicenter, prospective study. Patients received anagrelide at a starting dose of 0.5 mg twice per day, which was then adjusted for each patient.

RESULTS

Treatment with anagrelide resulted in a rapid decrease in the platelet count, from a median baseline platelet count of 743 x 10(9)/L to a median platelet count of 441 x 10(9)/L after 6 months (P < 0.0001). The proportion of patients with a platelet count < 600 x 10(9)/L increased from 30% at baseline to 77% after the 6-month study period. The rate of major thrombotic complications significantly decreased from 5% to 2% (P = 0.2568). For patients with essential thrombocythemia, the reduction of major thromboembolic complications was significant (P = 0.0455). The rate of minor thromboembolic complications decreased from 25% before anagrelide treatment to 14% during anagrelide treatment (P = 0.0278). No severe side effects were observed during the study period. There was, however, evidence that concomitant administration of acetylsalicylic acid may increase bleeding tendency.

CONCLUSIONS

Anagrelide was an effective and well tolerated treatment modality for reducing platelet counts in both newly diagnosed and pretreated patients with thrombocytosis due to myeloproliferative disorders.

Oral anticoagulants as secondary prophylaxis of thrombosis in patients with polycythemia vera: a retrospective analysis of 15 patients

Thrombotic complications are the leading cause of mortality in patients with polycythemia vera (PV). Phlebotomy and myelosuppressive agents are able to reduce the frequency of thrombosis; however, despite adequate control of myeloproliferation, the thrombotic risk remains increased in PV. This has led to a search for additional antithrombotic agents suited to reduce the rate of thrombotic events in PV. We have retrospectively analyzed 15 patients with PV who received oral anticoagulants (OA) as secondary prophylaxis of thrombosis at our institution with the aim of investigating this treatment approach in patients with PV. Despite OA treatment, 2 (13%) of 15 patients displayed recurrent venous thromboembolism, 3 patients (20%) displayed recurrent arterial thromboembolism, whereas 1 patient (7%) developed recurrent restenosis/occlusion of a transjugular intrahepatic porto-systemic shunt (TIPSS) implanted because of an underlying Budd-Chiari syndrome. Three (20%) of 15 patients had a total of 5 bleeding events during OA treatment, two of which were major bleedings. In none of the major bleedings over-anticoagulation was the reason for bleeding. Within the limitations of a retrospective analysis in a small number of patients, our data suggest that meticulous control of anticoagulant therapy is of critical importance in patients with PV, since in several of our patients recurrent thromboembolic events were associated with a low anticoagulation intensity of INR<2.0. In our opinion, a prospective clinical trial similar to the recently performed ECLAP study would be needed to more thoroughly elucidate the efficacy of OA in the secondary prophylaxis of thrombosis in PV.

Chronic myeloproliferative disorders

The Philadelphia chromosome-negative chronic myeloproliferative disorders (CMPD), polycythemia vera (PV), essential thrombocythemia (ET) and chronic idiopathic myelofibrosis (IMF), have overlapping clinical features but exhibit different natural histories and different therapeutic requirements. Phenotypic mimicry amongst these disorders and between them and nonclonal hematopoietic disorders, lack of clonal diagnostic markers, lack of understanding of their molecular basis and paucity of controlled, prospective therapeutic trials have made the diagnosis and management of PV, ET and IMF difficult. In Section I, Dr. Jerry Spivak introduces current clinical controversies involving the CMPD, in particular the diagnostic challenges. Two new molecular assays may prove useful in the diagnosis and classification of CMPD. In 2000, the overexpression in PV granulocytes of the mRNA for the neutrophil antigen NBI/CD177, a member of the uPAR/Ly6/CD59 family of plasma membrane proteins, was documented. Overexpression of PRV-1 mRNA appeared to be specific for PV since it was not observed in secondary erythrocytosis. At this time, it appears that overexpression of granulocyte PRV-1 in the presence of an elevated red cell mass supports a diagnosis of PV; absence of PRV-1 expression, however, should not be grounds for excluding PV as a diagnostic possibility. Impaired expression of Mpl, the receptor for thrombopoietin, in platelets and megakaryocytes has been first described in PV, but it has also been observed in some patients with ET and IMF. The biologic basis appears to be either alternative splicing of Mpl mRNA or a single nucleotide polymorphism, both of which involve Mpl exon 2 and both of which lead to impaired posttranslational glycosylation and a dominant negative effect on normal Mpl expression. To date, no Mpl DNA structural abnormality or mutation has been identified in PV, ET or IMF. In Section II, Dr. Tiziano Barbui reviews the best clinical evidence for treatment strategy design in PV and ET. Current recommendations for cytoreductive therapy in PV are still largely similar to those at the end of the PVSG era. Phlebotomy to reduce the red cell mass and keep it at a safe level (hematocrit < 45%) remains the cornerstone of treatment. Venesection is an effective and safe therapy and previous concerns about potential side effects, including severe iron deficiency and an increased tendency to thrombosis or myelofibrosis, were erroneous. Many patients require no other therapy for many years. For others, however, poor compliance to phlebotomy or progressive myeloproliferation, as indicated by increasing splenomegaly or very high leukocyte or platelet counts, may call for the introduction of cytoreductive drugs. In ET, the therapeutic trade-off between reducing thrombotic events and increasing the risk of leukemia with the use of cytoreductive drugs should be approached by patient risk stratification. Thrombotic deaths seem very rare in low-risk ET subjects and there are no data indicating that fatalities can be prevented by starting cytoreductive drugs early. Therefore, withholding chemotherapy might be justifiable in young, asymptomatic ET patients with a platelet count below 1500000/mm(3) and with no additional risk factors for thrombosis. If cardiovascular risk factors together with ET are identified (smoking, obesity, hypertension, hyperlipidemia) it is wise to consider platelet-lowering agents on an individual basis. In Section III, Dr. Gianni Tognoni discusses the role of aspirin therapy in PV based on the recently completed European Collaboration on Low-dose Aspirin in Polycythemia Vera (ECLAP) Study, a multi-country, multicenter project aimed at describing the natural history of PV as well as the efficacy of low-dose aspirin. Aspirin treatment lowered the risk of cardiovascular death, non-fatal myocardial infarction, and non-fatal stroke (relative risk 0.41 [95% CI 0.15-1.15], P =.0912). Total and cardiovascular mortality were also reduced by 46% and 59%, respectively. Major bleedings were slightly increased nonsignificnsignificantly by aspirin (relative risk 1.62, 95% CI 0.27-9.71). In Section IV, Dr. Giovanni Barosi reviews our current understanding of the pathophysiology of IMF and, in particular, the contributions of anomalous megakaryocyte proliferation, neoangiogenesis and abnormal CD34(+) stem cell trafficking to disease pathogenesis. The role of newer therapies, such as low-conditioning stem cell transplantation and thalidomide, is discussed in the context of a general treatment strategy for IMF. The results of a Phase II trial of low-dose thalidomide as a single agent in 63 patients with myelofibrosis with meloid metaplasia (MMM) using a dose-escalation design and an overall low dose of the drug (The European Collaboration on MMM) will be presented. Considering only patients who completed 4 weeks of treatment, 31% had a response: this was mostly due to a beneficial effect of thalidomide on patients with transfusion dependent anemia, 39% of whom abolished transfusions, patients with moderate to severe thrombocytopenia, 28% of whom increased their platelet count by more than 50 x 10(9)/L, and patients with the largest splenomegalies, 42% of whom reduced spleen size of more than 2 cm.