A prospective comparison between treatment with phlebotomy alone and with interferon-alpha in patients with polycythemia vera

Myeloproliferative neoplasms in the adolescent and young adult population: A comprehensive review of the literature

Myeloproliferative neoplasms (MPN) are characterized by a clonal proliferation of myeloid lineage cells within the bone marrow. The classical BCR-ABL negative MPNs are comprised of polycythaemia vera, essential thrombocythaemia and primary myelofibrosis. Historically, the majority of MPNs are diagnosed in adults older than 60 years of age; however, in recent years, there has been recognition of MPNs in the adolescent and young adult (AYA) population. AYAs with MPN, typically defined as between the ages of 15 and 39 years old, may comprise up to 20% of patients diagnosed with MPN. They demonstrate unique patterns of driver mutations and thrombotic events and remain at risk for progression to more aggressive disease states. Given the likely long length of time they will live with their disease, there is a significant unmet need in identifying well-tolerated and effective treatment options for these patients, particularly with the advent of disease modification. In this review, we provide a comprehensive overview of the clinical features, disease course and management of AYA patients with MPN and, in doing so, highlight key characteristics that distinguish them from their older counterparts.

Cytoreductive therapy in younger adults with polycythemia vera: a meta-analysis of safety and outcomes

ABSTRACT

Cytoreductive therapy is not routinely recommended for younger patients with polycythemia vera (PV) due to concern that treatment toxicity may outweigh therapeutic benefits. However, no systematic data support this approach. To support objective risk/benefit assessment of cytoreductive drugs in patients with PV aged <60 years (PV<60), this systematic review and meta-analysis was conducted to evaluate toxicity and disease-related complications in PV<60 treated with interferon alfa (rIFN-α) or hydroxyurea (HU). A search of PubMed, Scopus, Web of Science and Embase identified 693 unique studies with relevant keywords, of which 14 met inclusion criteria and were selected for analysis. The weighted average age of patients treated with rIFN-α was 48 years (n = 744 patients; 12 studies) and for HU was 56 years (n = 1397; 8 studies). The weighted average duration of treatment for either drug was 4.5 years. Using a Bayesian hierarchical model, the pooled annual rate of discontinuation due to toxicity was 5.2% for patients receiving rIFN-α (n = 587; 95% confidence interval [CI], 2.2-8.2) and 3.6% for HU (n = 1097; CI, 1-6.2). The average complete hematologic response for rIFN-α and HU was 62% and 52%, respectively. Patients experienced thrombotic events at a pooled annual rate of 0.79% and 1.26%; secondary myelofibrosis at 1.06% and 1.62%; acute myeloid leukemia at 0.14% and 0.26%; and death at 0.87% and 2.65%, respectively. No treatment-related deaths were reported. With acceptable rates of nonfatal toxicity, cytoreductive treatment, particularly with disease-modifying rIFN-α, may benefit PV<60. Future randomized trials prioritizing inclusion of PV<60 are needed to establish a long-term benefit of early cytoreductive treatment in these patients.

Recombinant Interferon-β in the Treatment of Polycythemia Vera and Related Neoplasms: Rationales and Perspectives

About 30 years ago, the first clinical trials of the safety and efficacy of recombinant interferon-α2 (rIFN-α2) were performed. Since then, several single-arm studies have shown rIFN-α2 to be a highly potent anticancer agent against several cancer types. Unfortunately, however, a high toxicity profile in early studies with rIFN-α2 -among other reasons likely due to the high dosages being used-disqualified rIFN-α2, which was accordingly replaced with competitive drugs that might at first glance look more attractive to clinicians. Later, pegylated IFN-α2a (Pegasys) and pegylated IFN-α2b (PegIntron) were introduced, which have since been reported to be better tolerated due to reduced toxicity. Today, treatment with rIFN-α2 is virtually outdated in non-hematological cancers, where other immunotherapies-e.g., immune-checkpoint inhibitors-are routinely used in several cancer types and are being intensively investigated in others, either as monotherapy or in combination with immunomodulatory agents, although only rarely in combination with rIFN-α2. Within the hematological malignancies, rIFN-α2 has been used off-label for decades in patients with Philadelphia-negative chronic myeloproliferative neoplasms (MPNs)-i.e., essential thrombocythemia, polycythemia vera, and myelofibrosis-and in recent years rIFN-α2 has been revived with the marketing of ropeginterferon-α2b (Besremi) for the treatment of polycythemia vera patients. Additionally, rIFN-α2 has been revived for the treatment of chronic myelogenous leukemia in combination with tyrosine kinase inhibitors. Another rIFN formulation-recombinant interferon-β (rIFN-β)-has been used for decades in the treatment of multiple sclerosis but has never been studied as a potential agent to be used in patients with MPNs, although several studies and reviews have repeatedly described rIFN-β as an effective anticancer agent as well. In this paper, we describe the rationales and perspectives for launching studies on the safety and efficacy of rIFN-β in patients with MPNs.

Stepping out of antiquity: An update on emerging drugs for the treatment of polycythemia vera

Introduction: Polycythemia vera is a chronic hematologic malignancy frequently presented with constitutional symptoms and associated with an increased risk of thrombosis, hemorrhage, and progression to myelofibrosis or acute myeloid leukemia. Current treatment strategies reduce thrombohemorrhagic risk by controlling blood counts and inhibiting platelets, but often fail to address disease-related symptoms or biologically modify the disease.Areas covered: We review the current paradigm for treating polycythemia vera, highlight areas of unmet need, review therapeutic agents in late stage clinical development, and provide an overarching view of how these emerging agent may fit into the future armamentarium of polycythemia vera treatments.Expert opinion: The shift from focusing solely on secondary prevention of thrombohemorrhagic events to a comprehensive treatment strategy that additionally aims to improve quality of life and prevent disease progression has resulted in a rapidly evolving therapeutic landscape that promises to move the treatment of polycythemia vera out of antiquity into the modern age.

Interferon-alpha for treating polycythemia vera yields improved myelofibrosis-free and overall survival

Interferon-alpha (rIFNα) is the only disease-modifying treatment for polycythemia vera (PV), but whether or not it prolongs survival is unknown. This large single center retrospective study of 470 PV patients compares the myelofibrosis-free survival (MFS) and overall survival (OS) with rIFNα to two other primary treatments, hydroxyurea (HU) and phlebotomy-only (PHL-O). The median age at diagnosis was 54 years (range 20-94) and the median follow-up was 10 years (range 0-45). Two hundred and twenty-nine patients were women (49%) and 208 were high-risk (44%). The primary treatment was rIFNα in 93 (20%), HU in 189 (40%), PHL-O in 133 (28%) and other cytoreductive drugs in 55 (12%). The treatment groups differed by ELN risk score (p < 0.001). In low-risk patients, 20-year MFS for rIFNα, HU, and PHL-O was 84%, 65% and 55% respectively (p < 0.001) and 20-year OS was 100%, 85% and 80% respectively (p = 0.44). In high-risk patients, 20-year MFS for rIFNα, HU, and PHL-O was 89%, 41% and 36% respectively (p = 0.19) and 20-year OS was 66%, 40%, 14% respectively (p = 0.016). In multivariable analysis, longer time on rIFNα was associated with a lower risk of myelofibrosis (HR: 0.91, p < 0.001) and lower mortality (HR: 0.94, p = 0.012). In conclusion, this study supports treatment of PV with rIFNα to prevent myelofibrosis and potentially prolong survival.

Ruxolitinib: a targeted treatment option for patients with polycythemia vera

Polycythemia vera (PV) is a chronic myeloproliferative neoplasm characterized by erythrocytosis and the presence of Janus kinase (JAK) 2V617F or similar mutations. This review summarizes the pathophysiology of PV, the challenges associated with traditional treatment options, and the scientific rationale and supportive clinical evidence for targeted therapy with ruxolitinib. Accumulating evidence indicates that activating mutations in JAK2 drive the PV disease state. Traditional PV treatment strategies, including aspirin, phlebotomy, and cytoreduc­tive agents such as hydroxyurea, provide clinical benefits for some but not all patients and may not adequately treat PV-related symptoms. Furthermore, traditional treatment approaches are associated with potential side effects that may limit their usage and lead some patients to discon­tinue the treatment. Ruxolitinib is an orally available small-molecule tyrosine kinase inhibitor that is a potent and selective inhibitor of JAK1/JAK2. Ruxolitinib is approved in the US for patients with PV with an inadequate response or intolerance to hydroxyurea and in Europe for adults with PV who are resistant to or intolerant of hydroxyurea. In the Phase III RESPONSE registration trial, ruxolitinib was superior to the best available therapy in patients with PV who were resistant to or intolerant of hydroxyurea in controlling hematocrit levels, reducing spleen volume, and improving PV-related symptoms and quality-of-life measures. The most common nonhematologic adverse events in ruxolitinib-treated patients were headache, diarrhea, pruritus, and fatigue in the RESPONSE trial; hematologic adverse events were primarily grade 1 or 2. In the Phase IIIb nonregistration RELIEF trial, there were nonsignificant trends toward an improved symptom control in patients with PV on a stable hydroxyurea dose who were generally well controlled but reported disease-associated symptoms and switched to ruxolitinib vs those who continued hydroxyurea therapy. Updated treatment guidelines will be important for educating physicians about the role of ruxolitinib in the treatment of patients with PV.

Ruxolitinib for the treatment of patients with polycythemia vera

Polycythemia vera (PV) is a hematopoietic proliferative disorder associated with Janus-associated kinase/signal transducer and activator of transcription pathway dysregulation resulting in erythrocytosis and, possibly, leukocytosis and thrombocytosis. Patients diagnosed with PV experience a broad range of symptoms associated with a reduced quality of life, often develop splenomegaly, and have an increased risk of death compared with age-matched subjects without PV. Current treatment options, notably hydroxyurea, help with disease management; however, insufficient efficacy or progressive resistance occurs in some patients, highlighting the need for new treatment options. Ruxolitinib is an oral JAK1/JAK2 inhibitor that has been evaluated in Phase II and III clinical trials in patients with PV, who are intolerant of or resistant to hydroxyurea. In this setting, ruxolitinib treatment has demonstrated normalization of blood cell counts, reduction in splenomegaly and improvements in PV-related symptom burden.

Novel and emerging therapies for the treatment of polycythemia vera

Polycythemia vera (PV) is a chronic myeloproliferative neoplasm defined by erythrocytosis and often accompanied by leukocytosis and thrombocytosis. Current treatment options, including IFN-α and hydroxyurea, effectively manage PV in many patients. However, some high-risk patients, particularly those who become hydroxyurea-intolerant/resistant, may benefit from IFN-α or new treatment options. A better understanding of PV pathophysiology, including the role of the JAK/STAT pathway, has inspired the development of new therapies. Several JAK inhibitors directly target JAK/STAT pathway activation and have been evaluated in Phase II/III trials with promising results. Pegylated variants of IFN-α, which reduce dosing frequency and toxicity associated with recombinant IFN-α, have yielded favorable efficacy results in Phase II trials. Finally, histone deacetylase inhibitors have been developed to manage PV at the level of chromatin-regulated gene expression. The earliest Phase III results from these next-generation therapies are expected in 2014.

Polycythemia vera: current pharmacotherapy and future directions

INTRODUCTION

In the past, management of polycythemia vera (PV) was built upon a cornerstone of control over erythrocytosis, through therapeutic phlebotomy, as well as the use of low-dose aspirin. Historically, selected patients were managed with additional cytoreductive therapies to decrease the risk of vascular events, with the recognition that these therapies likely did not impede progression.

AREAS COVERED

Recent clinical trials have demonstrated, in a randomized fashion, that optimal control of the hematocrit to target levels < 45% are important for decreasing the risk of vascular events. We are identifying that our historical set of cytoreductive agents, such as hydroxyurea, may be replaced in the future. The first candidate is pegylated interferon alpha-2a, which is demonstrating the ability to control vascular events and control extended hematopoiesis, while potentially having impact on fibrotic progression and Janus kinase 2 (JAK2) V1617F mutant allele burden. Ruxolitinib, as well as other JAK2 inhibitors in development, are demonstrating that this class of agents is making a very meaningful impact on the risk of vascular events in PV, controlling expanded hematopoiesis, as well as helping with symptomatic burden.

EXPERT OPINION

Future goals include attaining a better understanding of the specific roles of JAK inhibitor therapy and whether their use in combination with standard therapies offers greater efficacy than single agents alone.

Interferon-alpha targets JAK2V617F-positive hematopoietic progenitor cells and acts through the p38 MAPK pathway

OBJECTIVE

Interferon-alpha (IFNalpha) therapy leads to hematological remissions and a reduction of the JAK2V617F allele burden in patients with polycythemia vera (PV). In this study, the cellular target by which IFNalpha affects hematopoiesis in PV patients was evaluated.

MATERIALS AND METHODS

CD34(+) cells were isolated from normal bone marrow and the peripheral blood of patients with PV and were treated in vitro with each of the three commercially available forms of IFNalpha: IFNalpha 2b, pegylated IFNalpha 2a (Peg-IFNalpha 2a), and pegylated IFNalpha 2b (Peg-IFNalpha 2b).

RESULTS

Each form of IFNalpha was equally potent in suppressing hematopoietic colony formation by normal CD34(+) cells, but Peg-IFNalpha 2a and IFNalpha 2b were more effective than Peg-IFNalpha 2b in inhibiting burst-forming unit erythroid-derived colony formation by PV CD34(+) cells. In addition, exposure of PV CD34(+) cells to equal doses of Peg-IFNalpha 2a and IFNalpha 2b resulted in a 38% to 40% reduction in the proportion of JAK2V617F-positive hematopoietic progenitor cells (HPC), while equivalent doses of Peg-IFNalpha 2b did not reduce the number of malignant HPC. Further studies explored the mechanism by which IFNalpha induced PV HPC growth inhibition. Treatment of Peg-IFNalpha 2a increased the rate of apoptosis of PV CD34(+) cells and the phosphorylation/activation of p38 mitogen-activated protein kinase in PV CD34(+) cells, while the p38-specific inhibitor SB203580 reversed the growth inhibition and apoptosis induced by Peg-IFNalpha 2a.

CONCLUSION

These data suggest that low doses of IFNalpha selectively and directly suppress PV JAK2V617F HPC and that these agents act through the p38 mitogen-activated protein kinase pathway.

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.

Biomarker analysis in polycythemia vera under interferon-alpha treatment: clonality, EEC, PRV-1, and JAK2 V617F

Three consecutive polycythemia vera (PV) patients were analyzed before and during pegylated-interferon (rIFNalpha) treatment for the following markers: (1) granulocyte and CD34(+) cell clonality, (2) Jak2V617F expression, (3) PRV-1 mRNA overexpression, and (4) Epo-independent colony (EEC) growth. Before rIFNalpha therapy, all patients displayed clonal hematopoiesis, 100% Jak2V617F expression as well as PRV-1 overexpression, and EEC growth. After rIFNalpha treatment, all three patients demonstrated polyclonal hematopoiesis. Nonetheless, Jak2V617F expression, PRV-1 overexpression, and EEC-growth remained detectable, albeit at lower levels. We conclude that reemergence of polyclonal hematopoiesis after rIFNalpha treatment may be achieved in a substantial proportion of patients. However, this does not constitute elimination of the PV clone. These data demonstrate the usefulness of novel markers in monitoring minimal residual disease and caution against discontinuation of rIFNalpha treatment after hematologic remission. Long-term follow-up of large patient cohorts is required to determine whether rIFNalpha treatment can cause complete molecular remissions in PV.

Long-term effects of the treatment of polycythemia vera with recombinant interferon-alpha

Patients with polycythemia vera (PV) are most often treated with phlebotomy-only (PHL-O) or phlebotomy plus hydroxyurea (PHL + HU). Such treatment is often unsatisfactory because of persistent susceptibility to thrombosis owing to inadequate control of abnormal erythropoiesis and thrombopoiesis. Recombinant interferon-alpha (rIFN alpha) inhibits erythroid progenitors and affects megakaryocyte function and thus may be a more effective treatment, but reports of its use have been of relatively short duration. The long-term use (median, 13 years) of rIFN alpha in 55 patients previously treated with PHL alone or with PHL + HU was studied. Data pertaining to the natural history of the disease were also examined. Patients achieved partial response of their disease by 6 months, and complete response by 1-2 years (phlebotomy-free, HCT < or =45%, platelets < or =600,000/microL); spleen size was reduced in 27 of 30 patients with prior splenomegaly. The initial dose of rIFN alpha was 1 mega unit 3 times a week (1 MU/tiw) for the majority of patients, with periodic dose increases as required and as tolerated. The maintenance dose, usually 3 MU/tiw, could be decreased after the second year of treatment in half the patients. Toxicity was acceptable. Disease-free survival was marked by no thrombohemorrhagic complications reflecting both the effect of rIFN alpha and total patient care. Evidence is presented indicating that rIFN alpha effectively reduces PHL requirements, thrombocythemia, splenomegaly, and thrombohemorrhagic events. It is an effective drug for treating PV with acceptable toxicity.

Polycythemia vera

The differential diagnosis of an elevated hematocrit and the criteria for the diagnosis of polycythemia vera present little or no problem; however, there is not a consensus on therapy. Spivak likened this to a conundrum--"an intricate and difficult problem." Nonetheless, it can be argued that on the basis of the following criteria--life expectancy, the absence of toxicity, and long remissions an average of 3.1 years or a median of 2 years--and with acute leukemia no more common than in other regimens except phlebotomy alone (a regimen that cannot be sustained), 32P should be the treatment of choice except in pregnant women. Others, but not all, share this view. This is in contrast to the statement, "Thus chemotherapy treatment of [polycythemia vera] patients is not as easy, innocuous, and well tolerated as it is generally believed". Patients treated with phlebotomy alone were subjected to an unacceptably high incidence of early thrombotic events. Unavailability of pipobroman eliminates this choice.

Current management of polycythemia vera

Over a century has elapsed since the first description of polycythemia vera (PV), and current treatment recommendations are primarily based on the results of clinical trials that were performed in the late 1960s and early 1970s. Continued identification and appropriate utilization of PV-specific biologic parameters may allow substantial modification of early diagnostic criteria. New cytoreductive treatment agents are increasingly being used without any evidence of superiority over conventional therapy. The role of aspirin is being readdressed by an ongoing controlled study. Transformation of PV into either myelofibrosis with myeloid metaplasia or acute leukemia remains a major complication that may not be influenced by current therapy.

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

The effect of interferon alpha (IFN) on myeloproliferation and vascular complications was studied in 32 patients (17 female, 15 male; median age 60.5 yr) with polycythemia vera (PV). IFN therapy was initiated at a median time of 19 months after diagnosis. Ten patients were pretreated with chemotherapy in addition to phlebotomy. IFN dose was 12 megaU/wk during the first year, 9 megaU/wk during the second year and 12 megaU/wk thereafter. During IFN alpha treatment hematocrit level was 45.7% and remained at this level after the second year of treatment, compared to 46.5% before IFN. The frequency of phlebotomy before IFN was 0.49/month and dropped to 0.19/month (p <0.0005) during the first year of IFN treatment. IFN normalized high platelet and leukocyte counts in a majority of patients. The incidence of deep venous thromboses was 3.6%/yr before IFN alpha and 1.8%/yr during the first year of treatment. IFN-induced side-effects were mainly flu-like symptoms, fever, fatigue and arthralgia. In conclusion, IFN allowed the reduction of the dose of chemotherapy and decreased the need of phlebotomy. Despite improvement of hematological parameters, it is still uncertain whether IFN alpha can improve clinical symptoms in PV.

Treatment of polycythaemia vera and essential thrombocythaemia

The clinical course in both polycythaemia vera (PV) and essential thrombocythaemia (ET) is characterized by significant thrombohaemorrhagic complications and variable risk of disease transformation into myeloid metaplasia with myelofibrosis or acute myeloid leukaemia. Randomized studies have shown that the risk of thrombosis was significantly reduced in ET with the use of hydroxyurea (HU) and in PV with the use of chlorambucil or 32P. However, the use of chlorambucil or 32P has been associated with an increased risk of leukaemic transformation. Subsequently, other studies have suggested that both HU and pipobroman may be less leukaemogenic and as effective as chlorambucil and 32P for preventing thrombosis in PV. However, the results from these prospective studies have raised concern that even HU and pipobroman may be associated with excess leukaemic events in both ET and PV. The recent introduction of anagrelide as a specific platelet-lowering agent, the demonstration of treatment efficacy with interferon-alpha, and the revived interest in using low-dose acetylsalicylic acid provide the opportunity to initiate prospective randomized studies incorporating these treatments.

Long term treatment of myeloproliferative disease with interferon-alpha-2b: feasibility and efficacy

BACKGROUND

Recombinant interferon-alpha-2b (rIFN-alpha-2b) has shown therapeutic potential in patients with chronic myelogenous leukemia and other myeloproliferative disorders (MPDs), including the ability to suppress the abnormal hematopoietic clone and to reverse myelofibrosis. This study was conducted to evaluate further the efficacy and safety of rIFN-alpha-2b in a large group of patients with polycythemia vera, essential thrombocythemia, or agnogenic myeloid metaplasia and to determine maintenance of response after treatment discontinuation.

METHODS

Induction therapy began with subcutaneous rIFN-alpha-2b at 5.0 x 10(6) IU/day until a complete or partial response was achieved. Treatment continued at 2.5 x 10(6) IU/day until spleen size and hematologic parameters stabilized.

RESULTS

Fifty-four patients were studied (median follow-up, 7.3 years); at last follow-up 27 patients still were participating (median follow-up, 3.8 years). Twenty-four of 24 patients with thrombocythemia (100%) and 14 of 14 patients with hyperleukocytosis (100%) responded to induction therapy, whereas 26 of 39 patients (67%) experienced > 10% decrease in splenomegaly. Thirty-nine of 54 patients (72%) maintained response for a median of 39 weeks after withdrawal of rIFN-alpha-2b; repeat courses in previously responding patients produced similar results. The survival rate at 8 years was 60%. rIFN-alpha-2b generally was well tolerated, but toxicity caused treatment withdrawal in 7 patients (13%).

CONCLUSIONS

rIFN-alpha-2b can produce regression of splenomegaly and control of leukocyte and platelet counts in patients with MPD. These responses are sustained for prolonged periods in some patients after therapy discontinuation. In patients with recurrent disease, disease control can be attained again with reinitiation of rIFN-alpha-2b. Therefore this therapy should be an important treatment consideration for patients with MPD.

Long-term therapeutic efficacy and toxicity of recombinant interferon-alpha 2a in polycythaemia vera

We report on long-term therapeutic efficacy and toxicity of recombinant interferon-alpha 2a (rIFN-alpha) in a series of 38 patients with polycythaemia vera (PV). In all patients haematocrit was first brought into the normal range by venesection; rIFN-alpha was then begun at a starting weekly dose of 9,000,000 IU. Complete response (CR) was defined as persistence of normal haematocrit without venesection and partial response (PR) as >50% reduction of phlebotomy requirement. Eleven patients (28.9%) achieved CR and 8 (21.0%) PR. Median duration of treatment for all responsive patients was 40 months; 12 patients are still responsive and under treatment after 13, 15, 25, 35, 40, 41, 43, 49, 50, 51, 52 and 52 months of therapy with rIFN-alpha. In responsive patients, rIFN-alpha also normalized leucocyte counts, platelet counts and spleen enlargement; rIFN-alpha also relieved generalized pruritus in all 10 patients displaying this symptom. Early toxicity (flu-like syndrome) was observed in 23.6% and late toxicity (severe weakness) in 13.1% of patients, requiring rIFN-alpha treatment suspension in all cases. Progression to leukaemia was observed in none of the 10 patients treated only with rIFN-alpha and in one of the 12 who received alkylating agents before enrolment in this study. According to these data, rIFN-alpha seems to be an effective and safe treatment option for PV.

Polycythemia vera treated with recombinant interferon-alpha 2a: evidence of a selective effect on the malignant clone

We periodically analyzed bone-marrow cytogenetic features in 8 patients belonging to a series of 38 subjects with polycythemia vera (PV), all treated with recombinant interferon-alpha 2a (rIFN-alpha) at a weekly dose of 9,000,000 IU. Six out of these 8 patients never showed any chromosome alterations, while 2 displayed at diagnosis the presence of trisomy 8 in all bone-marrow metaphases. Interestingly enough, in these 2 patients rIFN-alpha treatment was able to induce not only complete hematological response but also the disappearance of trisomy 8, as shown by conventional cytogenetic investigation and fluorescence in situ hybridization performed on bone-marrow cells after 1 year of treatment. This finding indicates that, as previously shown in chronic myeloid leukemia, in PV rIFN-alpha can also eradicate the malignant clone by means of a selective effect on bone-marrow transformed cells.

New drugs in essential thrombocythemia and polycythemia vera

Among the chronic myeloproliferative disorders, polycythemia vera and essential thrombocythemia are unique because of their association with thrombohemorrhagic manifestations and their relatively indolent clinical course. Patients with essential thrombocythemia may not have a significant shortening of life-expectancy and most may not require specific therapy. However, patients with polycythemia vera have a significant risk of transformation of polycythemia vera into acute leukemia or postpolycythemic myelofibrosis (or both). 'High-risk-for-thrombosis' patients with either polycythemia vera or essential thrombocythemia require specific therapy with a platelet-lowering agent to prevent thrombotic complications. Currently, the standard agent used for this is hydroxyurea. However, its tetratogenic and leukemogenic potential has been of concern. As a result, new platelet-lowering agents are being evaluated in the treatment of polycythemia vera and essential thrombocythemia. Anagrelide and interferon alfa are two such agents and have been shown to be effective in reducing platelet counts in patients with chronic myeloproliferative disorders. The putative mechanism of action of these drugs, their specific activity in polycythemia vera and essential thrombocythemia, side-effect profile, and current indications are discussed herein.

The role of alpha-interferon in essential thrombocythaemia, polycythaemia vera and myelofibrosis with myeloid metaplasia (MMM): a concise update

Treatment of essential thrombocythaemia (ET), polycythaemia vera (PV), and myelofibrosis with myeloid metaplasia (MMM) patients is frequently a difficult issue. To date, there is no generally accepted treatment for these diseases which can reduce the risk of thromboembolism and/or haemorrhagic events, avoid any increase in the frequency of secondary myelofibrosis and terminal blast transformation and decrease the reticulin content in the bone marrow of MMM patients. The most frequently used myelosuppressive agent is hydroxyurea (HU), but widespread application has failed to demonstrate that is not leukaemogenic. In patients with MMM, conflicting results have been obtained following alpha-IFN treatment. Haematological responses have been seen in 50% of the patients. Usually the patients showing good responses had a hyperproliferative type of disease. In only one case was a reduction of reticulin content of the bone marrow observed. Thus, these findings do not indicate alpha-IFN as a first-line therapy. On the other hand, the results of several reports in ET and PV patients have shown a reduction in the abnormal proliferation of megakaryocytes and erythroid elements, following alpha-IFN treatment. A reduction in spleen size has also frequently been seen. Together with the improvement of haematological parameters, clinical symptoms have also responded positively. Long term control of these diseases can be obtained with a well-tolerated low dose of alpha-IFN. However, PV and ET are not usually characterized by cytogenetic abnormalities, making it very difficult to demonstrate the disappearance of clonal haemopoiesis following alpha-IFN therapy, even if this does occasionally occur, as evident from the two cytogenetic convertions described in the literature. As compared to myelosuppressive drugs or phlebotomy, alpha-IFN thus represents an attractive new treatment, able to exert a fundamental influence on these diseases, presumably without any untoward leukaemogenic or gonadotoxic activity.