Allogeneic stem cell transplantation for myelofibrosis in 2012

The 2020 revision of the guidelines for the management of myeloproliferative neoplasms

In 2016, the World Health Organization revised the diagnostic criteria for myeloproliferative neoplasms (MPNs) based on the discovery of disease-driving genetic aberrations and extensive analysis of the clinical characteristics of patients with MPNs. Recent studies have suggested that additional somatic mutations have a clinical impact on the prognosis of patients harboring these genetic abnormalities. Treatment strategies have also advanced with the introduction of JAK inhibitors, one of which has been approved for the treatment of patients with myelofibrosis and those with hydroxyurea-resistant or intolerant polycythemia vera. Recently developed drugs aim to elicit hematologic responses, as well as symptomatic and molecular responses, and the response criteria were refined accordingly. Based on these changes, we have revised the guidelines and present the diagnosis, treatment, and risk stratification of MPNs encountered in Korea.

HLA-mismatched donor and high ferritin level showed poor clinical outcomes after allogeneic hematopoietic cell transplantation in patients with advanced myelofibrosis

Background:

Preconditioning intensity, donor choice and graft-versus-host disease (GVHD) prophylaxis of allogeneic hematopoietic cell transplantation (allo-HCT) for advanced myelofibrosis (MF) have not been fully elucidated.

Methods:

Thirty-five patients with advanced MF were treated with reduced-intensity conditioning (RIC) allo-HCT. We searched for matched sibling donors first, followed by matched or mismatched unrelated donors and familial mismatched donors. Preconditioning regimen consisted of fludarabine (total 150 mg/m²) and busulfan (total 6.4 mg/kg) with total body irradiation ⩽400cGy.

Results:

All showed engraftments, but four showed either leukemic relapse or delayed graft failure. Two-year overall survival (OS) and non-relapse mortality (NRM) was 60.0% and 29.9%, respectively. Acute GVHD was observed in 19 patients, and grade III–IV acute GVHD (eight grade III and four grade IV) was higher in human leukocyte antigen (HLA)-mismatched donor HCT compared with HLA-matched HCT (70% versus 20%). Chronic GVHD was observed in 16 patients, and a cumulative incidence of severe chronic GVHD was 33% in HLA-mismatched donor HCT and 7.7% in HLA-matched HCT. Significant hepatic GVHD was observed in nine patients (five acute, four chronic) and six of them died. Multivariate analysis revealed inferior OS in HLA-mismatched donor HCT (hazard ratio (HR) = 6.40, 95% confidence interval (CI) 1.6–25.7, p = 0.009) and in patients with high ferritin level at the time of pre-conditioning period (HR = 7.22, 95% CI 1.9–27.5, p = 0.004), which were related to higher incidence of hepatic GVHD with high NRM rate.

Conclusion:

RIC allo-HCT can be a valid choice providing graft-versus-fibrosis effect for advanced MF patients. However, HLA-mismatched donor and high pre-HCT ferritin level related to fatal hepatic GVHD should be regarded as poor-risk parameters.

Primary myelofibrosis marrow-derived CD14+/CD34- monocytes induce myelofibrosis-like phenotype in immunodeficient mice and give rise to megakaryocytes

To confirm that neoplastic monocyte-derived collagen- and fibronectin-producing fibrocytes induce bone marrow (BM) fibrosis in primary myelofibrosis (PMF), we injected PMF BM-derived fibrocyte-precursor CD14⁺/CD34^- monocytes into the tail vein of NOD-SCID-γ (NSG) mice. PMF BM-derived CD14⁺/CD34^- monocytes engrafted and induced a PMF-like phenotype with splenomegaly, myeloid hyperplasia with clusters of atypical megakaryocytes, persistence of the JAK2^V617F mutation, and BM and spleen fibrosis. As control we used normal human BM-derived CD14⁺/CD34^- monocytes. These monocytes also engrafted and gave rise to normal megakaryocytes that, like PMF CD14⁺/CD34^--derived megakaryocytes, expressed HLA-ABC and human CD42b antigens. Using 2 clonogenic assays we confirmed that PMF and normal BM-derived CD14⁺/CD34^- monocytes give rise to megakaryocyte colony-forming cells, suggesting that a subpopulation BM monocytes harbors megakaryocyte progenitor capacity. Taken together, our data suggest that PMF monocytes induce myelofibrosis-like phenotype in immunodeficient mice and that PMF and normal BM-derived CD14⁺/CD34^- monocytes give rise to megakaryocyte progenitor cells.

Impact of ruxolitinib pretreatment on outcomes after allogeneic stem cell transplantation in patients with myelofibrosis

INTRODUCTION

Ruxolitinib is the first approved drug for treatment of myelofibrosis, but its impact of outcome after allogeneic stem cell transplantation (ASCT) is unknown.

PATIENTS AND METHODS

We reported on 159 myelofibrosis patients (pts) with a median age of 59 years (r: 28-74) who received reduced intensity ASCT between 2000 and 2015 in eight German centers from related (n = 23), matched (n = 86) or mismatched (n = 50) unrelated donors. Forty-six (29%) patients received ruxolitinib at any time point prior to ASCT. The median daily dose of ruxolitinib was 30 mg (range 10-40 mg) and the median duration of treatment was 4.9 months (range 0.4-39.1 months).

RESULTS

Primary graft failure was seen in 2 pts (4%) in the ruxolitinib and 3 (2%) in the non-ruxolitinib group. Engraftment and incidence of acute GVHD grade II to IV and III/IV did not differ between groups (37% vs 39% and 19% vs 28%, respectively), nor did the non-relapse mortality at 2 years (23% vs 23%). A trend for lower risk of relapse was seen in the ruxolitinib group (9% vs 17%, P = .2), resulting in a similar 2 year DFS and OS (68% vs 60% and 73% vs 70%, respectively). No difference in any outcome variable could be seen between ruxolitinib responders and those who failed or lost response to ruxolitinib.

CONCLUSIONS

These results suggest that ruxolitinib pretreatment in myelofibrosis patient does not negatively influence outcome after allogeneic stem cell transplantation.

Recent advances in the diagnosis and management of primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) in which dysregulation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathways is the major pathogenic mechanism. Most patients with PMF carry a driver mutation in the JAK2, MPL (myeloproliferative leukemia), or CALR (calreticulin) genes. Mutations in epigenetic regulators and RNA splicing genes may also occur, and play critical roles in PMF disease progression. Based on revised World Health Organization diagnostic criteria for MPNs, both screening for driver mutations and bone marrow biopsy are required for a specific diagnosis. Clinical trials of JAK2 inhibitors for PMF have revealed significant efficacy for improving splenomegaly and constitutional symptoms. However, the currently available drug therapies for PMF do not improve survival. Although allogeneic stem cell transplantation is potentially curative, it is associated with substantial treatment-related morbidity and mortality. PMF is a heterogeneous disorder and decisions regarding treatments are often complicated, necessitating the use of prognostic models to determine the management of treatments for individual patients. This review focuses on the clinical aspects and outcomes of a cohort of Japanese patients with PMF, including discussion of recent advances in the management of PMF.

Outcome of patients with Myelofibrosis relapsing after allogeneic stem cell transplant: a retrospective study by the Chronic Malignancies Working Party of EBMT

Allogeneic Haematopoietic Stem Cell Transplant (allo-HSCT) remains the only curative approach for Myelofibrosis (MF). Scarce information exists in the literature on the outcome and, indeed, management of those MF patients who relapse following transplant. We hereby report on the management and outcome of 202 patients who relapsed post allo-HSCT for MF.

Myeloproliferative neoplasm stem cells

Myeloproliferative neoplasms (MPNs) arise in the hematopoietic stem cell (HSC) compartment as a result of the acquisition of somatic mutations in a single HSC that provides a selective advantage to mutant HSC over normal HSC and promotes myeloid differentiation to engender a myeloproliferative phenotype. This population of somatically mutated HSC, which initiates and sustains MPNs, is termed MPN stem cells. In >95% of cases, mutations that drive the development of an MPN phenotype occur in a mutually exclusive manner in 1 of 3 genes: JAK2, CALR, or MPL The thrombopoietin receptor, MPL, is the key cytokine receptor in MPN development, and these mutations all activate MPL-JAK-STAT signaling in MPN stem cells. Despite common biological features, MPNs display diverse disease phenotypes as a result of both constitutional and acquired factors that influence MPN stem cells, and likely also as a result of heterogeneity in the HSC in which MPN-initiating mutations arise. As the MPN clone expands, it exerts cell-extrinsic effects on components of the bone marrow niche that can favor the survival and expansion of MPN stem cells over normal HSC, further sustaining and driving malignant hematopoiesis. Although developed as targeted therapies for MPNs, current JAK2 inhibitors do not preferentially target MPN stem cells, and as a result, rarely induce molecular remissions in MPN patients. As the understanding of the molecular mechanisms underlying the clonal dominance of MPN stem cells advances, this will help facilitate the development of therapies that preferentially target MPN stem cells over normal HSC.

The role of JAK1/2 inhibitors in the treatment of chronic myeloproliferative neoplasms

In 2005, the description of the JAK2V617F mutation for the first time provided a molecular key to enable more rapid diagnosis and target for novel therapeutics in the myeloproliferative neoplasms. In 2007, the first-in-class agent INC18424, ruxolitinib, JAKafi, or JAKAVI was first tested in patients with intermediate-risk 2 or high-risk myelofibrosis regardless of whether they possessed the JAK2V617F mutation. Patients treated with this agent had major reduction in splenomegaly as well as impressive reduction, and in some cases resolution, of symptoms. This study was followed by the two Controlled Myelofibrosis Study with Oral JAK Inhibitor Therapy (COMFORT) trials (the first-ever phase III trials in myelofibrosis), which confirmed results in these aspects were superior to either placebo or standard care, and updated results show a survival advantage with this therapy. This paper discusses these results and data from other JAK inhibitors while speculating on the future of these therapies. It also reflects on the fact that the true targets and agents' mode of action are uncertain. Unlike targeted therapy for chronic myeloid leukemia (CML), these agents do not deliver molecular remission, and it is not clear whether their predominant benefit is mediated via JAK2, JAK1, or both. Nonetheless, the advent of the JAK inhibitor is a welcome advance and has made a dramatic improvement to the therapeutic landscape of these conditions.

Pacritinib: a new agent for the management of myelofibrosis?

INTRODUCTION

Myelofibrosis (MF) is a clonal haematological disease associated with recurrent somatic gene mutations (JAK2V617F, MPL, CALR) and constitutive activation of the Janus kinase (JAK)/Signal Transducer and Activator of Transcription pathway. MF is often characterised by debilitating symptoms and JAK inhibitors (JAKIs) have revolutionised available therapeutic options. Ruxolitinib, a JAK1 and 2 inhibitor, is the only currently approved agent. Several other JAKIs are undergoing evaluation in the clinical trial setting and Pacritinib , a novel JAK2 and FLT3 inhibitor, is at an advanced stage of investigation with recent completion of a Phase III trial and another ongoing.

AREAS COVERED

Within this article we focus on pacritinib, summarising the development, preclinical and up-to-date results from the Phase I - III trials. We present the most recent data on efficacy and safety and indirectly compare this novel JAKI with ruxolitinib.

EXPERT OPINION

The kinome array data for pacritinib suggests that it has a range of targets differing to those for ruxolitinib. Pacritinib appears to be an effective agent for the control of MF-related symptoms and splenomegaly with potentially fewer haematological side-effects when compared with ruxolitinib and seems a particularly promising agent for anaemic and thrombocytopenic patients. It is also an attractive drug for potential combination studies due to its good tolerability.

Guidelines for the management of myeloproliferative neoplasms

Polycythemia vera, essential thrombocythemia, and primary myelofibrosis are collectively known as 'Philadelphia-negative classical myeloproliferative neoplasms (MPNs).' The discovery of new genetic aberrations such as Janus kinase 2 (JAK2) have enhanced our understanding of the pathophysiology of MPNs. Currently, the JAK2 mutation is not only a standard criterion for diagnosis but is also a new target for drug development. The JAK1/2 inhibitor, ruxolitinib, was the first JAK inhibitor approved for patients with intermediate- to high-risk myelofibrosis and its effects in improving symptoms and survival benefits were demonstrated by randomized controlled trials. In 2011, the Korean Society of Hematology MPN Working Party devised diagnostic and therapeutic guidelines for Korean MPN patients. Subsequently, other genetic mutations have been discovered and many kinds of new drugs are now under clinical investigation. In view of recent developments, we have revised the guidelines for the diagnosis and management of MPN based on published evidence and the experiences of the expert panel. Here we describe the epidemiology, new genetic mutations, and novel therapeutic options as well as diagnostic criteria and standard treatment strategies for MPN patients in Korea.

Outcomes of Allogeneic Hematopoietic Cell Transplantation in Patients with Myelofibrosis with Prior Exposure to Janus Kinase 1/2 Inhibitors

The impact of Janus kinase (JAK) 1/2 inhibitor therapy before allogeneic hematopoietic cell transplantation (HCT) has not been studied in a large cohort in myelofibrosis (MF). In this retrospective multicenter study, we analyzed outcomes of patients who underwent HCT for MF with prior exposure to JAK1/2 inhibitors. One hundred consecutive patients from participating centers were analyzed, and based on clinical status and response to JAK1/2 inhibitors at the time of HCT, patients were stratified into 5 groups: (1) clinical improvement (n = 23), (2) stable disease (n = 31), (3) new cytopenia/increasing blasts/intolerance (n = 15), (4) progressive disease: splenomegaly (n = 18), and (5) progressive disease: leukemic transformation (LT) (n = 13). Overall survival (OS) at 2 years was 61% (95% confidence interval [CI], 49% to 71%). OS was 91% (95% CI, 69% to 98%) for those who experienced clinical improvement and 32% (95% CI, 8% to 59%) for those who developed LT on JAK1/2 inhibitors. In multivariable analysis, response to JAK1/2 inhibitors (P = .03), dynamic international prognostic scoring system score (P = .003), and donor type (P = .006) were independent predictors of survival. Among the 66 patients who remained on JAK1/2 inhibitors until stopped for HCT, 2 patients developed serious adverse events necessitating delay of HCT and another 8 patients had symptoms with lesser severity. Adverse events were more common in patients who started tapering or abruptly stopped their regular dose ≥6 days before conditioning therapy. We conclude that prior exposure to JAK1/2 inhibitors did not adversely affect post-transplantation outcomes. Our data suggest that JAK1/2 inhibitors should be continued near to the start of conditioning therapy. The favorable outcomes of patients who experienced clinical improvement with JAK1/2 inhibitor therapy before HCT were particularly encouraging, and need further prospective validation.

Improved Outcome of Alternative Donor Transplantations in Patients with Myelofibrosis: From Unrelated to Haploidentical Family Donors

This is a retrospective analysis of 95 patients with myelofibrosis who were allografted between 2001 and 2014. The aims of the study were to assess whether the outcome of alternative donor grafts has improved with time and how this compares with the outcome of identical sibling grafts. Patients were studied in 2 time intervals: 2000 to 2010 (n = 58) and 2011 to 2014 (n = 37). The Dynamic International Prognostic Scoring System score was comparable in the 2 time periods, but differences in the most recent group included older age (58 versus 53 years, P = .004), more family haploidentical donors (54% versus 5%, P < .0001), and the introduction of the thiotepa-fludarabine-busulfan conditioning regimen (70% of patients versus 2%, P < .0001). Acute and chronic graft-versus-host disease were comparable in the 2 time periods. The 3-year transplantation-related mortality (TRM) in the 2011 to 2014 period versus the 2000 to 2010 period is 16% versus 32% (P = .10), the relapse rate 16% versus 40% (P = .06), and actuarial survival 70% versus 39% (P = .08). Improved survival was most pronounced in alternative donor grafts (69% versus 21%, P = .02), compared with matched sibling grafts (72% versus 45%, P = .40). In conclusion, the outcome of allografts in patients with myelofibrosis has improved in recent years because of a reduction of both TRM and relapse. Improvement is most significant in alternative donor transplantations, with modifications in donor type and conditioning regimen.

Janus Kinase Inhibitors and Stem Cell Transplantation in Myelofibrosis

Myelofibrosis (MF) is characterized by splenomegaly, blood count abnormalities, particularly cytopenias, and a propensity for transformation to acute leukemia. The current treatment approach is to ameliorate symptoms due to these abnormalities. Treatment with Janus kinase 2 inhibitors reduces spleen size and improves symptoms in patients with MF, but most of the patients eventually have disease progression and stop responding. Allogeneic stem cell transplantation remains the only curative option. However, its efficacy must be balanced against the risk of treatment-related death and long-term sequelae of transplant like chronic graft versus host disease. The challenge is to integrate treatment with Janus kinase inhibitors with allogeneic stem cell transplantation.

Clinical potential of pacritinib in the treatment of myelofibrosis

Myelofibrosis (MF) is a myeloid disorder caused by a clonal hematopoietic stem-cell proliferation associated with activation of the Janus kinase (JAK) signal transducer and activator of transcription (STAT) signaling pathways. Patients with MF often develop severe splenomegaly, marked symptom burden and significant cytopenias, with a consequent marked negative impact on quality of life and survival. The management of MF patients has dramatically improved with the development of a group of drugs that inhibit JAK signaling. The first of these agents to be approved was ruxolitinib, a JAK1/JAK2 inhibitor, which has been shown to improve both spleen size and symptoms in patients with MF. However, myelotoxicity, particularly of the platelet lineage, significantly limits the patient population who can benefit from this agent. Thus, there is an unmet need for novel agents with limited myelotoxicity to treat MF. Pacritinib, a JAK2 and FMS-like tyrosine kinase 3 (FLT3) inhibitor, has shown promising results in early phase trials with limited myelotoxicity and clinical responses that are comparable with those seen with ruxolitinib, even in patients with severe thrombocytopenia. Currently there are two large phase III clinical trials of pacritinib in MF, including patients with thrombocytopenia, and those previously treated with ruxolitinib. If the encouraging results observed in early phase clinical trials are confirmed, pacritinib will represent a new and exciting treatment option for patients with MF and particularly patients with significant cytopenias.

Effect of conditioning regimens on graft failure in myelofibrosis: a retrospective analysis

In myelofibrosis, the introduction of reduced-intensity conditioning (RIC) preceding allogeneic stem cell transplantation (SCT) resulted in lower transplant-related mortality rates compared with myeloablative conditioning. However, lowering the intensity of conditioning may increase the risk of graft failure in myelofibrosis, although hitherto this has not been indisputably proven. We here report the outcome of 53 patients who underwent allogeneic SCT with different conditioning regimens (RIC and non-myeloablative (NMA)) in three transplantation centers in the Netherlands. The cumulative incidence of graft failure within 60 days after SCT was high (28%), and this was primarily associated with the intensity of the conditioning regimen. Cumulative neutrophil engraftment at 60 days was lower in patients who received NMA conditioning compared with those who received RIC (56% vs 84%, P=0.03). Furthermore, of six patients who received a second transplantation after graft failure, the three patients with RIC regimens subsequently engrafted, whereas the three patients who received a second NMA regimen did not. This study indicates that in myelofibrosis, NMA regimens result in high engraftment failure rates. We propose the use of more intensive conditioning regimens, incorporating busulfan or melphalan.

Janus kinase inhibitors and allogeneic stem cell transplantation for myelofibrosis

Myelofibrosis (MF) is a manifestation of several disorders of hematopoiesis, collectively referred to as myeloproliferative neoplasms. Allogeneic hematopoietic stem cell transplantation (ASCT) is the only therapy with proven curative potential. However, most patients with MF are in their 6th or 7th decade of life, and only some of these patients have been considered suitable transplantation candidates. The development of reduced-intensity conditioning regimens with limited toxicity has allowed clinicians to offer ASCT to a growing number of older patients. The availability of Janus Kinase (JAK) 1/2 inhibitors allows clinicians to provide symptom relief and improved quality of life for MF patients. These drugs may also affect the decision regarding, in particular, the timing of ASCT. Future studies need to address the role of JAK1/2 inhibitors in patients who are transplantation candidates and determine their role before and, possibly, after transplantation. The identification of indications for the use of JAK1/2 inhibitors in the context of transplantation may lead to new therapeutic strategies for patients with MF.

Acute respiratory distress syndrome in a patient with primary myelofibrosis after ruxolitinib treatment discontinuation

Ruxolitinib is a Janus kinase (JAK) inhibitor used for the treatment of myelofibrosis with demonstrated efficacy for the alleviation of disease-related symptoms and splenomegaly. Anemia and thrombocytopenia are the main secondary effects. However, there are case reports of rare but serious adverse events following drug withdrawal. We present a case of a 76-year-old man diagnosed with primary myelofibrosis who presented with constitutional symptoms and symptomatic splenomegaly. Ruxolitinib was started (15 mg twice daily) and his disease-related symptoms disappeared. Six weeks later, he developed grade 4 thrombocytopenia and grade 3 anemia. Ruxolitinib was stopped and corticosteroid treatment (prednisone 1 mg/kg/day) was started to avoid a cytokine-rebound reaction. The patient then developed fever, chills, a biological inflammatory syndrome, and an acute respiratory disease syndrome. Full workup excluded an infection and we concluded that ruxolitinib withdrawal syndrome was the likely cause. Continued treatment with corticosteroids, as well as oxygen supply and continuous positive airway pressure, allowed an alleviation of his symptoms. This case report describes acute respiratory distress syndrome as another potential complication of ruxolitinib withdrawal syndrome.

Allogeneic hematopoietic cell transplantation for myelofibrosis using fludarabine-, intravenous busulfan- and low-dose TBI-based conditioning

Graft failure is one of the major barriers to the success of allogeneic hematopoietic cell transplantation (HCT) in myelofibrosis (MF). We report our institutional experience with 27 MF patients who underwent HCT using fludarabine-, intravenous BU- and low-dose total body irradiation (FBT)-based reduced-intensity (n=20) or full-intensity (n=7) conditioning regimens. Eight patients had prior exposure to JAK1/2 inhibitor therapy; six patients received JAK1/2 inhibitors leading on to HCT and two patients received transplant at the failure of JAK1/2 inhibitor therapy. No adverse impact of JAK1/2 inhibitor therapy was observed on early post-transplant outcomes. All evaluable patients had neutrophil recovery, and no primary graft failure was observed. Cumulative incidence of grades II-IV acute GVHD at day 100 was 48% (95% confidence interval (CI), 29-67%) and chronic GVHD at 2 years was 66% (95% CI, 49-84%). Cumulative incidences of nonrelapse mortality (NRM), relapse and probability of OS at 2 years were: 43% (95% CI, 12-74%), 10% (95% CI, 0-39%) and 56% (95% CI, 28-77%), respectively. FBT-based conditioning regimen has a favorable impact on engraftment; however, further efforts are required to reduce NRM.

MPD-RC 101 prospective study of reduced-intensity allogeneic hematopoietic stem cell transplantation in patients with myelofibrosis

From 2007 to 2011, 66 patients with primary myelofibrosis or myelofibrosis (MF) preceded by essential thrombocythemia or polycythemia vera were enrolled into a prospective phase 2 clinical trial of reduced-intensity allogeneic hematopoietic stem cell transplantation (AHSCT), Myeloproliferative Disorder Research Consortium 101 trial. The study included patients with sibling donors (n = 32) receiving fludarabine/melphalan (FluMel) as a preparative regimen and patients with unrelated donors (n = 34) receiving conditioning with FluMel plus anti-thymocyte globulin (ATG). Patient characteristics in the 2 cohorts were similar. Engraftment occurred in 97% of siblings and 76% of unrelated transplants, whereas secondary graft failure occurred in 3% and 12%, respectively. With a median follow-up of 25 months for patients alive, the overall survival (OS) was 75% in the sibling group (median not reached) and 32% in the unrelated group (median OS: 6 months, 95% confidence interval [CI]: 3, 25) (hazard ratio 3.9, 95% CI: 1.8,8.9) (P < .001). Nonrelapse mortality was 22% in sibling and 59% in unrelated AHSCT. Survival correlated with type of donor, but not with the degree of histocompatibility match, age, or JAK2(V617F) status. In patients with MF with sibling donors, AHSCT is an effective therapy, whereas AHSCT from unrelated donors with FluMel/ATG conditioning led to a high rate of graft failure and limited survival. This trial was registered at www.clinicaltrials.gov as #NCT00572897.

Increasing therapeutic efficacy in MPN

In this issue of Blood, Bhagwat et al describe an elegant series of experiments showing that genetic deletion in the hematopoietic system of Janus kinase 2 (JAK2) abrogates initiation of myeloproliferative disease and substantial disease regression if deleted once disease is initiated.

Safety evaluation of ruxolitinib for treating myelofibrosis

INTRODUCTION

In 2005, the JAK2 V617F mutation was identified and found to be highly prevalent in the 'Philadephia Chromosome-negative' Myeloproliferative neoplasms (MPN). This led to new diagnostic criteria for MPN in addition to the development of the first targeted therapy for myelofibrosis (MF), ruxolitinib .

AREAS COVERED

Ruxolitinib was approved within 5 years of 'first-in-man' trials; it has been assessed in two large Phase III trials, and to date, several thousand patients have been prescribed this drug. This article reviews the latest data from the Phase III trials concerning efficacy and safety in addition to post-authorisation data for this agent. Ruxolitinib is an extremely well-tolerated drug; it is associated with bruising, headaches, dizziness, anaemia and thrombocytopaenia. In addition, an augmented risk of infections has been documented.

EXPERT OPINION

Ruxolitinib has radically altered the therapeutic landscape for MF with demonstrated advantages over standard therapy, irrespective of JAK2 mutational status and a signal suggesting survival benefit. Other JAK inhibitors are also in late stages of development, although the furthest advanced has just been withdrawn due to cases of encephalopathy (not documented with ruxolitinib). This reminds the clinical community of the need for post-marketing surveillance of safety for these agents. Challenges ahead are identification of appropriate surrogates for survival benefit and perhaps how to best use ruxolitinib either alone or in combination with other therapies.

Allogeneic transplantation for myelofibrosis: for whom, when, and what are the true benefits?

PURPOSE OF REVIEW

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only potentially curative therapy for myelofibrosis. Despite improved outcomes, morbidity and mortality of HSCT remain high. Here we examine recent data on patient selection, timing, and outcomes of HSCT in myelofibrosis.

RECENT FINDINGS

While there is a general effort to restrict HSCT to transplant-eligible intermediate-2 and high-risk patients, this group has comparatively worse HSCT outcomes, largely driven by their high transplant-related mortality (TRM). When adjusted for age, reduced intensity conditioning (RIC) has shown superior outcomes compared with myeloablative conditioning (MAC), making RIC-HSCT a viable option for older patients. Emerging concepts include the use of ruxolitinib pretransplant, optimizing MAC to decrease toxicity, and use of posttransplant JAK2-mutant allele burden to guide prophylactic immunotherapy to prevent relapse. The recognition of prognostic significance of somatic mutations in the ASXL1, EZH2, SRSF2, and IDH1/2 genes, and the improved assessment of risk of leukemic transformation have added a new dimension to risk stratification.

SUMMARY

Improving our understanding of molecular genetics and leukemic transformation holds promise for more precise patient selection for HSCT. Although RIC-HSCT may reduce TRM, further studies are needed to optimize conditioning regimens and to define the optimal timing of HSCT.

Allogeneic hematopoietic stem cell transplantation in patients with polycythemia vera or essential thrombocythemia transformed to myelofibrosis or acute myeloid leukemia: a report from the MPN Subcommittee of the Chronic Malignancies Working Party of the European Group for Blood and Marrow Transplantation

The clinical course of polycythemia vera and essential thrombocythemia is potentially associated with long-term severe complications, such as evolution to myelofibrosis or acute myeloid leukemia. Allogeneic stem cell transplantation is currently the only potentially curative treatment for advanced polycythemia vera or essential thrombocythemia. We analyzed 250 consecutive patients with an initial diagnosis of polycythemia vera (n=120) or essential thrombocythemia (n=130), who underwent transplantation due to progression to myelofibrosis (n=193) or acute myeloid leukemia (n=57) and who were reported to the European Group for Blood and Marrow Transplantation registry between 1994 and 2010. Their median age was 56 years (range, 22-75) and in 52% of cases the interval between diagnosis and transplantation was 10 years or more. With a median follow-up from transplantation of 13 months, the 3-year overall survival rate and relapse incidence were 55% and 32%, respectively. In univariate analysis, the main parameters that negatively affected post-transplantation outcomes were older age (>55 years), a diagnosis at transplant of acute myeloid leukemia and the use of an unrelated donor. The overall 3-year cumulative incidence of non-relapse mortality was 28%, but was significantly higher in older patients than in younger ones (>55 years, 35% versus 20%, P=0.032), in those transplanted from an unrelated donor rather than a related donor (34% versus 18%, P=0.034) and in patients with a diagnosis of acute myeloid leukemia compared to myelofibrosis (29% versus 27%, P=0.045). This large retrospective study confirms that transplantation is potentially curative for patients with end-stage polycythemia vera/essential thrombocythemia progressing to myelofibrosis or acute myeloid leukemia. Relapse and non-relapse mortality remain unsolved problems for which innovative treatment approaches need to be assessed.

VPS 45-associated primary infantile myelofibrosis--successful treatment with hematopoietic stem cell transplantation

PMF of infancy is a recently described autosomal recessive disorder presenting with severe bone marrow failure, accelerated neutrophil apoptosis, and significant platelet dysfunction, caused by a mutation in the VPS45 gene. In this study, we update our group of patients with PMF, highlighting different aspects of this disease, and evaluating the effectiveness of HSCT for the treatment of this disorder. Update of clinical data, hematological features, molecular studies, treatment and final outcome of four children diagnosed with VPS 45-associated PMF of infancy. The patients described had clinical and hematological findings consistent with MF. Molecular studies showed that all patients were homozygous for the Thr224Asn mutation in the VPS 45 gene. HSCT was carried out in three patients and was successful in two. VPS 45-associated MF is a novel primary immune deficiency that can be successfully corrected by HSCT if applied early in the course of disease using appropriate conditioning. The diagnosis of VPS 45-associated PMF should be considered in all children presenting with SCN with subsequent development of pancytopenia. Long-term follow-up of these patients is necessary to identify extra-hematological manifestations of VPS45 deficiency.

Allogeneic transplantation for primary myelofibrosis with BM, peripheral blood or umbilical cord blood: an analysis of the JSHCT

To determine whether a difference in donor source affects the outcome of transplantation for patients with primary myelofibrosis (PMF), a retrospective study was conducted using the national registry data on patients who received first allogeneic hematopoietic cell transplantation (HCT) with related BM (n=19), related PBSCs (n=25), unrelated BM (n=28) or unrelated umbilical cord blood (UCB; n=11). The 5-year OS rates after related BM, related PBSC and unrelated BM transplantation were 63%, 43% and 41%, respectively, and the 2-year OS rate after UCB transplantation was 36%. On multivariate analysis, the donor source was not a significant factor for predicting the OS rate. Instead, performance status (PS) ⩾2 (vs PS 0–1) predicted a lower OS (P=0.044), and RBC transfusion ⩾20 times before transplantation (vs transfusion ⩽9 times) showed a trend toward a lower OS (P=0.053). No advantage of nonmyeloablative preconditioning regimens in terms of decreasing nonrelapse mortality or increasing OS was found. Allogeneic HCT, and even unrelated BM and UCB transplantation, provides a curative treatment for PMF patients.

[Primary myelofibrosis--pathogenesis, diagnosis and treatment]

BACKGROUND

Primary myelofibrosis is a malignant myeloproliferative disease. It is characterised by proliferation of megakaryocytes in the bone marrow, dysregulated cytokine production and reactive fibrosis that causes bone marrow failure. The purpose of this article is to provide an up-to-date presentation of the pathophysiology, diagnostics and treatment of the disease.

METHOD

The article is based on the authors' own experience and on a selection of articles identified through many years of experience of treating patients with myelofibrosis.

RESULTS

The molecular mechanisms that trigger the disease remain unidentified, but mutations in two genes (JAK2 and MPL) occur in 70% of patients and result in increased production of haematopoietic cells. Diagnosis is based on clinical examination, bone marrow histology and molecular biological examinations. The clinical course of primary myelofibrosis varies. Life expectancy depends on a number of factors and is severely decreased by high-risk disease. Allogeneic stem cell transplantation is the only treatment with a curative potential, but only a minority of patients are eligible for it. If transplantation is not possible, therapy is symptomatic. JAK2-inhibitors are new drugs that counteract cytokine production and cell proliferation. Ruxolitinib is the first approved JAK2 inhibitor and has proved effective on symptoms and quality of life.

INTERPRETATION

Medical inhibition of the JAK2 gene and associated JAK-STAT signalling pathway is a step forward in treatment. However, stem cell transplantation remains the only potentially curative treatment for myelofibrosis.

Resolution of bone marrow fibrosis in a patient receiving JAK1/JAK2 inhibitor treatment with ruxolitinib

Ruxolitinib, a JAK1/JAK2 inhibitor, is currently the only pharmacological agent approved for the treatment of myelofibrosis. Approval was based on findings from two phase 3 trials comparing ruxolitinib with placebo (COMFORT-I) and with best available therapy (COMFORT-II) for the treatment of primary or secondary myelofibrosis. In those pivotal trials, ruxolitinib rapidly improved splenomegaly, disease-related symptoms, and quality of life and prolonged survival compared with both placebo and conventional treatments. However, for reasons that are currently unclear, there were only modest histomorphological changes in the bone marrow, and only a subset of patients had significant reductions in JAK2 V617F clonal burden. Here we describe a patient with post-polycythemia vera myelofibrosis who received ruxolitinib at our institution (Guy's and St. Thomas' NHS Foundation Trust, London, United Kingdom) as part of the COMFORT-II study. While on treatment, the patient had dramatic improvements in splenomegaly and symptoms shortly after starting ruxolitinib. With longer treatment, the patient had marked reductions in JAK2 V617F allele burden, and fibrosis of the bone marrow resolved after approximately 3 years of ruxolitinib treatment. To our knowledge, this is the first detailed case report of resolution of fibrosis with a JAK1/JAK2 inhibitor.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00934544.

Treatment and management of myelofibrosis in the era of JAK inhibitors

Myelofibrosis (MF) can present as a primary disorder or evolve from polycythemia vera (PV) or essential thrombocythemia (ET) to post-PV MF or post-ET MF, respectively. MF is characterized by bone marrow fibrosis, splenomegaly, leukoerythroblastosis, extramedullary hematopoiesis, and a collection of debilitating symptoms. Until recently, the therapeutic options for patients with MF consisted of allogeneic hematopoietic stem cell transplant (alloHSCT), the use of cytoreductive agents (ie, hydroxyurea), splenectomy and splenic irradiation for treatment of splenomegaly, and management of anemia with transfusions, erythropoiesis-stimulating agents (ESAs), androgens, and immunomodulatory agents. However, with increased understanding of the pathogenesis of MF resulting from dysregulated Janus kinase (JAK) signaling, new targeted JAK inhibitor therapies, such as ruxolitinib, are now available. The purpose of this article is to review the clinical features of MF, discuss the use and future of JAK inhibitors, reassess when and how to use conventional MF treatments in the context of JAK inhibitors, and provide a perspective on the future of MF treatment.

Update on the treatment of Ph-negative myeloproliferative neoplasms

SUMMARY Myeloproliferative neoplasms (MPNs) that do not harbor the BCR–ABL rearrangement include polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis. All of these diseases are characterized by an increased risk of vascular complications and by the propensity to evolve into acute leukemia. The JAK2V617F mutation determines a gain of function in the gene encoding JAK2 and is the most frequent molecular abnormality in MPNs, with an estimated prevalence of more than 95% in PV and 50% in ET and primary myelofibrosis. Molecular markers, together with marrow histology and cytogenetic data, are increasingly relevant for MPN diagnosis, and their prognostic value is under evaluation. In PV and ET, the use of aspirin, hydroxyurea and phlebotomy remain the mainstay of treatment. In myelofibrosis, conventional therapy (androgens, steroids, chemotherapy and splenectomy) has still only palliative effects. The only potentially curative approach is allogeneic stem cell transplantation, but treatment-related mortality remains high. In the last 2 years, the JAK–STAT pathway has become the target of selective tyrosine kinase inhibitors, which might represent a promising therapeutic option. Their role in future therapy, as single agents and/or in combinatorial approaches, is yet to be determined.

Comprehensive review of JAK inhibitors in myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem-cell disorders, characterized phenotypically by the abnormal accumulation of mature-appearing myeloid cells. Polycythemia vera, essential thrombocythemia, primary myelofibrosis (also known as 'BCR-ABL1-negative' MPNs), and chronic myeloid leukemia (CML) are the primary types of MPNs. After the discovery of the BCR-ABL1 fusion protein in CML, several oncogenic tyrosine kinases have been identified in 'BCR-ABL1-negative' MPNs, most importantly, JAK2V617F mutation. The similarity in the clinical characteristics of the BCR-ABL1-negative MPN patients along with the prevalence of the Janus kinase mutation in this patient population provided a strong rationale for the development of a new class of pharmacologic inhibitors that target this pathway. The first of its class, ruxolitinib, has now been approved by the food and drug administration (FDA) for the management of patients with intermediate- to high-risk myelofibrosis. Ruxolitinib provides significant and sustained improvements in spleen related and constitutional symptoms secondary to the disease. Although noncurative, ruxolitinib represents a milestone in the treatment of myelofibrosis patients. Other types of JAK2 inhibitors are being tested in various clinical trials at this point and may provide better efficacy data and safety profile than its predecessor. In this article, we comprehensively reviewed and summarized the available preclinical and clinical trials pertaining to JAK inhibitors.

Do different conditioning regimens really make a difference?

Over the past 15 years, the use of reduced-intensity/nonmyeloablative conditioning regimens before allogeneic hematopoietic stem cell transplantation has been increasing. Despite major disparities in the level of myeloablation, intensity of immunosuppression (including great diversity of in vivo T-cell depletion), and postgraft immunomodulation, the different approaches have contributed jointly to a modification of the stage of allogeneic stem cell transplantation: transplantation-related procedure mortality has been decreased dramatically, allowing allogeneic immunotherapy to be used in previously excluded populations, including elderly patients, young but clinically unsuitable patients, patients with lymphoid malignancies or solid tumors, and patients without an HLA-identical related or unrelated donor. Together, these diverse regimens have provided one of the biggest breakthroughs since the birth of allogeneic BM transplantation. However, consensus on how to reach the optimal goal of minimal transplantation-related mortality with maximum graft-versus-tumor effect is far from being reached, and further studies are needed to define optimal conditioning and immunomodulatory regimens that can be integrated to reach this goal. These developments, which will most likely vary according to different clinical situations, have to be compared continuously with advances achieved in traditional allogeneic transplantation and nontransplantation treatments. However, the lack of prospective comparative trials is and will continue to make this task challenging.

Ruxolitinib: a potent and selective Janus kinase 1 and 2 inhibitor in patients with myelofibrosis. An update for clinicians

Ruxolitinib became the first US Food and Drug Administration approved therapy for myelofibrosis in 2011 and EU approval is anticipated in summer 2012. Two large phase III trials (known as the COMFORT studies) were the basis for this approval and were published recently. In this review article we discuss the challenges in managing myelofibrosis, the information to date about ruxolitinib and speculate as to the future direction with this and similar agents.

Role of additional novel therapies in myeloproliferative neoplasms

The recent approval of ruxolitinib (INCB018424) for myelofibrosis and the preclinical/clinical development of several additional janus kinase (JAK)-targeted agents have ushered in an era of novel therapies for advanced myeloproliferative neoplasms (MPN), which are associated with constitutive activation of the JAK-signal transducer and activation of transcription (STAT) signaling pathway. Collectively, these novel therapeutic approaches could rapidly broaden the spectrum of available therapies, with potential for improved clinical outcome for patients with advanced MPN. This review covers the recent developments in the testing of novel therapeutic agents other than JAK inhibitors that target signaling pathways in addition to JAK/STAT, or target the deregulated epigenetic mechanisms in MPN.