Interim analysis of safety and efficacy of ruxolitinib in patients with myelofibrosis and low platelet counts

Ten years after ruxolitinib approval for myelofibrosis: a review of clinical efficacy

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm characterized by splenomegaly, abnormal cytokine expression, cytopenias, and progressive bone marrow fibrosis. The disease often manifests with burdensome symptoms and is associated with reduced survival. Ruxolitinib, an oral Janus kinase (JAK) 1 and JAK2 inhibitor, was the first agent approved for MF. As a first-in-class targeted treatment, ruxolitinib approval transformed the MF treatment approach and remains standard of care. In addition, targeted inhibition of JAK1/JAK2 signaling, a key molecular pathway underlying MF pathogenesis, and the large volume of literature evaluating ruxolitinib, have led to a better understanding of the disease and improved management in general. Here we review ruxolitinib efficacy in patients with MF in the 10 years following approval, including demonstration of clinical benefit in the phase 3 COMFORT-I/II trials, real-world evidence, translational studies, and expanded access data. Lastly, future directions for MF treatment are discussed, including ruxolitinib-based combination therapies.

Efficacy and safety of ruxolitinib in patients with myelofibrosis and low platelet count (50 × 109/L to <100 × 109/L) at baseline: the final analysis of EXPAND

Background:

Thrombocytopenia is a common feature of myelofibrosis (MF), a myeloproliferative neoplasm driven by dysregulated JAK/STAT signaling; however, pivotal trials assessing the efficacy of ruxolitinib (a JAK1/2 inhibitor) excluded MF patients with low platelet counts (<100 × 10⁹/L).

Objectives:

Determination of the maximum safe starting dose (MSSD) of ruxolitinib was the primary endpoint, with long-term safety and efficacy as secondary and exploratory endpoints, respectively.

Design:

EXPAND (NCT01317875) was a phase 1b, open-label, ruxolitinib dose-finding study in patients with MF and low platelet counts (50 to <100 × 10⁹/L).

Methods:

Patients were stratified according to baseline platelet count into stratum 1 (S1, 75 to <100 × 10⁹/L) or stratum 2 (S2, 50 to <75 × 10⁹/L). Previous analyses established the MSSD at 10 mg twice daily (bid); long-term results are reported here.

Results:

Of 69 enrolled patients, 38 received ruxolitinib at the MSSD (S1, n = 20; S2, n = 18) and are the focus of this analysis. The incidence of adverse events was consistent with the known safety profile of ruxolitinib, with thrombocytopenia (S1, 50%; S2, 78%) and anemia (S1, 55%; S2, 44%) the most frequently reported adverse events and no new or unexpected safety signals. Substantial clinical benefits were observed for patients in both strata: 50% (10/20) and 67% (12/18) of patients in S1 and S2, respectively, achieved a spleen response (defined as ⩾50% reduction in spleen length from baseline) at any time during the study.

Conclusion:

The final safety and efficacy results from EXPAND support the use of a 10 mg bid starting dose of ruxolitinib in patients with MF and platelet counts 50 to <100 × 10⁹/L.

Registration:

ClinicalTrials.gov NCT01317875.

Myeloproliferative Neoplasms, Version 3.2022, NCCN Clinical Practice Guidelines in Oncology

The classic Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) consist of myelofibrosis, polycythemia vera, and essential thrombocythemia and are a heterogeneous group of clonal blood disorders characterized by an overproduction of blood cells. The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for MPN were developed as a result of meetings convened by a multidisciplinary panel with expertise in MPN, with the goal of providing recommendations for the management of MPN in adults. The Guidelines include recommendations for the diagnostic workup, risk stratification, treatment, and supportive care strategies for the management of myelofibrosis, polycythemia vera, and essential thrombocythemia. Assessment of symptoms at baseline and monitoring of symptom status during the course of treatment is recommended for all patients. This article focuses on the recommendations as outlined in the NCCN Guidelines for the diagnosis of MPN and the risk stratification, management, and supportive care relevant to MF.

Pacritinib for the treatment of patients with myelofibrosis and thrombocytopenia

INTRODUCTION

: Myelofibrosis (MF) is a rare myeloproliferative neoplasm characterized by a complex symptom profile, cytopenias, splenomegaly, and potential for leukemic progression. Severe thrombocytopenia is common in patients with MF and correlates with poor prognosis; however, until recently, treatment options for these patients were limited. Pacritinib, a potent Janus kinase (JAK) 2/interleukin-1 receptor-associated kinase 1 (IRAK1) inhibitor, has demonstrated significant reduction in splenomegaly, improved symptom control, and a manageable safety profile in patients with MF regardless of the severity of thrombocytopenia.

AREAS COVERED

: This review will outline the pacritinib drug profile and summarize key efficacy and safety data, focusing on the 200 mg twice daily dose from phase 2 and 3 studies that formed the basis for the recent US Food and Drug Administration approval of pacritinib in patients with MF and severe thrombocytopenia (platelet counts <50 x 10⁹/L).

EXPERT OPINION

Pacritinib, with its unique mechanism of action targeting both JAK2 and IRAK1, offers patients with MF and severe thrombocytopenia a new treatment option, providing consistent disease and symptom control. Adverse events are easily manageable. Further analyses to identify ideal patient characteristics for pacritinib and other JAK inhibitors along with studies of pacritinib combinations are warranted, including in related myeloid malignancies.

Fedratinib, the first selective JAK2 inhibitor approved for treatment of myelofibrosis - an option beyond ruxolitinib

Introduction: Myelofibrosis, a life shortening clonal disorder, presents with a constellation of features: bone marrow fibrosis, abnormal blood counts, extramedullary hematopoiesis, splenomegaly, thrombohemorrhagic complications and constitutional symptoms. Until recently Ruxolitinib, a JAK1 and 2 inhibitor, has been the only targeted therapy available for transplant-ineligible patients requiring treatment for splenomegaly and disease related symptoms. However, most patients discontinue Ruxolitinib after 3-5 years, mostly due to loss of response. There has been an unmet need for this patient group. In August 2019 Fedratinib (INREBIC® capsules, Impact Biomedicines, Inc., a wholly owned subsidiary of Bristol Meyer Squibb), a JAK2 inhibitor, was approved by US FDA for treatment of myelofibrosis in both JAK inhibitor naïve and pre-treated patients for the management of symptoms and splenomegaly.Areas covered: Here, we discuss the development, evidence base to date for Fedratinib. Including early and late phase, and ongoing trials, safety issues, potential role and current position of Fedratinib in the treatment of myelofibrosis, as well as future direction of targeted therapy in myelofibrosis.Expert opinion: Fedratinib presents a much needed option of treatment, particularly, for patients failing Ruxolitinib, with response rates that are quite similar. Nonetheless, there remain important questions including sequencing and options for combining therapy.

Thrombocytopenia in Patients With Myelofibrosis: Pathogenesis, Prevalence, Prognostic Impact, and Treatment

Myelofibrosis (MF) is a clonal hematopoietic stem cell neoplasm, characterized by pathologic myeloproliferation associated with inflammatory and pro-angiogenic cytokine release, that results in functional compromise of the bone marrow. Thrombocytopenia is a disease-related feature of MF, which portends a poor prognosis impacting overall survival (OS) and leukemia free survival. Thrombocytopenia in MF has multiple causes including ineffective hematopoiesis, splenic sequestration, and treatment-related effects. Presently, allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curable treatment for MF, which, unfortunately, is only a viable option for a minority of patients. All other currently available therapies are either focused on improving cytopenias or the alleviating systemic symptoms and burdensome splenomegaly. While JAK2 inhibitors have moved to the forefront of MF therapy, available JAK inhibitors are advised against in patients with severe thrombocytopenia (platelets < 50 × 10⁹/L). In this review, we describe the pathogenesis, prevalence, and prognostic significance of thrombocytopenia in MF. We also explore the value and limitations of treatments directed at addressing cytopenias, splenomegaly and symptom burden, and those with potential disease modification. We conclude by proposing a treatment algorithm for patients with MF and severe thrombocytopenia.

Ruxolitinib combined with prednisone, thalidomide and danazol in patients with myelofibrosis: Results of a pilot study

Ruxolitinib is a safe and effective therapy of myeloproliferative neoplasm-associated (MPN) myelofibrosis. However, often there are dose reductions and/or therapy interruptions because of therapy-related adverse events (AEs), especially anemia and thrombocytopenia. We previously reported combined therapy with prednisone, thalidomide and danazol (PTD) reversed anemia and thrombocytopenia in people with MPN-associated myelofibrosis. We wondered whether adding PTD to ruxolitinib might mitigate the hematologic AEs and thereby avoid the dose reduction of ruxolitinib and improve the efficacy. To test this hypothesis, we conducted a baseline hemoglobin and platelet concentration assignment prospective observational study in 72 patients comparing 3-month dose adjustment and efficacy of ruxolitinib with (N = 53, the study group) or without (N = 19, the control group) PTD. According to the platelet counts, the median daily ruxolitinib doses in the study group increased from 30 to 40 mg by week 12, whereas in the control group it remained at 30 mg (p = 0.019). In the study group 35 patients had a hemoglobin increase ≥10 g/L compared with no patient receiving ruxolitinib only (p < 0.001). Platelet increases >100 × 10E+9/L were seen in 56.6% and 5.3% of patients in the two groups, respectively (p < 0.001). In patients with anemia and thrombocytopenia, 18 patients in the study group had an anemia response at week 12 and 12 had a platelet increase of ≥50 × 10E+9/L. No patient in the control group achieved either response (p < 0.001 and p = 0.078). The study group had a more spleen response than the control group (p = 0.046). Peripheral edema and transaminase elevation were the main nonhematologic AEs of PTD. These AEs can be alleviated by adjusting the danazol dose. In conclusion, adding PTD to ruxolitinib improved ruxolitinib-associated anemia and thrombocytopenia, and resulted in a higher ruxolitinib dose.

Safety and Efficacy of Ruxolitinib in Patients with Myelofibrosis and Low Platelet Counts (50 - 100 × 109/L): Final Analysis of an Open-Label Phase 2 Study

INTRODUCTION

Treatment options in patients with myelofibrosis (MF) presenting with thrombocytopenia are limited. Final results of the phase 2 study (NCT01348490) of ruxolitinib in patients with MF and low baseline platelet counts (50 - 100 × 10⁹/L) are reported.

PATIENTS AND METHODS

Patients received ruxolitinib 5 mg twice daily (BID), with optional up-titration to a maximum of 15 mg BID, provided platelet count remained ≥40 × 10⁹/L. Assessments included spleen volume and length, Total Symptom Score (TSS), quality of life, and safety.

RESULTS

Of 66 patients, 52 (78.8%) completed the first 24 weeks of treatment. Median (range) percentage change from baseline in spleen volume and TSS (coprimary endpoints) were -20.5% (-55.8% to 38.5%, n=51) and -39.8% (-98.6% to 226.4%, n=53), respectively; greatest median reductions were in the 10 mg BID final titrated dose group. Of patients achieving ≥35% or ≥10% reduction in spleen volume, 8/11 (72.7%) and 21/34 (61.8%), respectively, were in the 10 mg BID final titrated dose group. Thirty-seven of 65 patients (56.9%) had ≥20% improvement in TSS, and 35/66 patients (53.0%) were Patient Global Impression of Change responders. Treatment-emergent adverse events led to dose interruption in 17/66 patients (25.8%), most commonly thrombocytopenia (n=3).

CONCLUSION

A starting dose of ruxolitinib 5 mg BID with gradual up-titration and dose optimization based on hematologic parameters and response was efficacious and generally well-tolerated in patients with MF and low platelet counts. Median improvement in spleen volume and symptoms was greatest for patients receiving ruxolitinib 10 mg BID.

Safety and efficacy of fedratinib, a selective oral inhibitor of Janus kinase-2 (JAK2), in patients with myelofibrosis and low pretreatment platelet counts

Fedratinib, an oral Janus kinase‐2 (JAK2) inhibitor, is approved for patients with myelofibrosis (MF) and platelet counts ≥50 × 10⁹/l, based on outcomes from the phase 3, placebo‐controlled JAKARTA trial in JAK‐inhibitor‐naïve MF, and the phase 2, single‐arm JAKARTA2 trial in patients previously treated with ruxolitinib. We evaluated the efficacy and safety of fedratinib 400 mg/day in patients with baseline platelet counts 50 to <100 × 10⁹/l (“Low‐Platelets” cohorts), including 14/96 patients (15%) in JAKARTA and 33/97 (34%) in JAKARTA2. At 24 weeks, spleen response rates were not significantly different between the Low‐Platelets cohort and patients with baseline platelet counts ≥100 × 10⁹/l (“High‐Platelets” cohort), in JAKARTA (36% vs. 49%, respectively; p = 0.37) or JAKARTA2 (36% vs. 28%; p = 0.41). Symptom response rates were also not statistically different between the Low‐ and High‐Platelets cohorts. Fedratinib was generally well‐tolerated in both platelet‐count cohorts. New or worsening thrombocytopaenia was more frequent in the Low‐Platelets (44%) versus the High‐Platelets (9%) cohort, but no serious thrombocytopaenia events occurred. Thrombocytopaenia was typically managed with dose modifications; only 3/48 Low‐Platelets patients discontinued fedratinib due to thrombocytopaenia. These data indicate that fedratinib 400 mg/day is safe and effective in patients with MF and low pretreatment platelet counts, and no initial fedratinib dose adjustment is required for these patients.

Role of JAK inhibitors in myeloproliferative neoplasms: current point of view and perspectives

Classic Philadelphia-negative myeloproliferative neoplasms (MPN) include polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF), classified as primary (PMF), or secondary to PV or ET. All MPN, regardless of the underlying driver mutation in JAK2/CALR/MPL, are invariably associated with dysregulation of JAK/STAT pathway. The discovery of JAK2V617F point mutation prompted the development of small molecules inhibitors of JAK tyrosine kinases (JAK inhibitors-JAKi). To date, among JAKi, ruxolitinib (RUX) and fedratinib (FEDR) are approved for intermediate and high-risk MF, and RUX is also an option for high-risk PV patients inadequately controlled by or intolerant to hydroxyurea. While not yet registered, pacritinib (PAC) and momelotinib (MMB), proved to be effective particularly in thrombocytopenic and anemic MF patients, respectively. In most cases, JAKi are effective in reducing splenomegaly and alleviating disease-related symptoms. However, almost 50% lose response by three years and dose-dependent toxicities may lead to suboptimal dosing or treatment discontinuation. To date, although not being disease-modifying agents, JAKi represent the therapeutic backbone particularly in MF patient. To optimize therapeutic strategies, many trials with drug combinations of JAKi with novel molecules are ongoing. This review critically discusses the role of JAKi in the modern management of patients with MPN.

Managing patients with myelofibrosis and thrombocytopenia

INTRODUCTION

: Given the progressive nature of myelofibrosis, the incidence of thrombocytopenia increases over time. Furthermore, approved drugs ruxolitinib and fedratinib, induce thrombocytopenia. Hence, treatment of myelofibrosis patients with low platelet counts is an unmet need.

AREAS COVERED

: This review summarizes the current and emerging treatment options available for patients with myelofibrosis and thrombocytopenia. In the first section of this review, we summarized the use of JAK inhibitors in patients with thrombocytopenia, and in the second part, we focused on use of therapies other than JAK Inhibitors such as steroids, immunomodulatory agents, androgens and other novel agents.

EXPERT OPINION

: Up to 25% of patients with myelofibrosis have platelet counts below 100,000 at presentation. Patients with thrombocytopenia are more likely to be anemic and PRBC transfusion-dependent, as well as have high-risk disease characteristics and a poor overall survival rate.. Among all JAK inhibitors studied in phase 3 clinical trials, pacritinib seems not to induce significant thrombocytopenia while maintaining a good spleen response. Severe thrombocytopenia is a major impediment to myelofibrosis therapy, and more research, particularly on novel therapeutic agents aimed at cytopenic patient populations, is needed.

Novel strategies for challenging scenarios encountered in managing myelofibrosis

Given its rarity, multi-faceted clinical presentation and the relative paucity of approved therapies, the management of myeloproliferative neoplasm (MPN)-associated myelofibrosis (MF) can be challenging. Janus kinase (JAK) inhibitors, the only approved agents at present, have brought many clinical benefits to patients, with prolongation of survival also demonstrated for ruxolitinib. However, these agents have clear limitations. Optimal management of anemia in MF remains a major unmet need. Neither ruxolitinib nor fedratinib is recommended for use in patients with severe thrombocytopenia, i.e. platelets <50 × 10⁹/L, who have a particularly poor prognosis. The search for the optimal partner for JAK inhibitors to address some of the shortcomings of these agents (e.g. limited ability to improve bone marrow fibrosis, cytopenias and induce molecular responses) and achieve meaningful 'disease modification' continues. This has led to the development of a number of rational, preclinically synergistic combinations for use either upfront or in the setting of sub-optimal response to JAK inhibition. Finally, the outlook for patients whose disease progresses on JAK inhibitor therapy continues to be grim, and agents with alternative mechanisms of action may be needed in this setting. In this article, we use a case-based approach to illustrate challenges commonly encountered in clinical practice and our management of the same. Fortunately, there has been enormous growth in drug development efforts in the MF space in the last few years, some of which appear poised to bear fruit in the very near future.

The effect of eltrombopag in managing thrombocytopenia associated with tyrosine kinase therapy in patients with chronic myeloid leukemia and myelofibrosis

Approximately 20-50% patients with chronic phase chronic myeloid leukemia (CML-CP) treated with tyrosine kinase inhibitors (TKIs) or with myelofibrosis (MF) treated with ruxolitinib develop grade ≥3 thrombocytopenia needing treatment interruptions and dose reductions. We conducted a non-randomized, phase II, single-arm study to determine the efficacy of eltrombopag for patients with CML or MF with persistent thrombocytopenia while on TKI or ruxolitinib. Eltrombopag was initiated at 50 mg/day, with dose escalation up to 300 mg daily allowed every 2 weeks. Twenty-one patients were enrolled (CML=15, MF=6); median age 60 years (range, 31-97 years). The median platelet count was 44x109/L (range, 3-49x109/L) in CML and 62x109/L (range, 21-75x109/L) in MF. After a median of 18 months (range, 5-77 months), 12/15 patients with CML achieved complete platelet response. The median peak platelet count among responders was 154x109/L (range, 74-893x109/L). Among CML patients 5 could re-escalate the TKI dose and 9 improved their response. None of the 6 patients with MF had a sustained response. Therapy was generally well tolerated. One patient discontinued therapy due to toxicity (elevated transaminases). One patient with CML developed significant thrombocytosis (>1000x109/L). Another CML patient developed non occlusive deep venous thrombosis in the right upper extremity without thrombocytosis, and one MF patient had myocardial infarction. Eltrombopag may help improve platelet counts in CML patients receiving TKI with recurrent thrombocytopenia. Further studies are warranted.

Patterns of Care for Older Patients With Myelofibrosis: A Population-based Study

BACKGROUND

Current treatments for myelofibrosis (MF) are largely palliative, with the JAK inhibitor ruxolitinib being the breakthrough approved for higher-risk patients by the United States Food and Drug Administration in November 2011. There are limited data on the "real-world" clinical experiences among patients with MF who are treated in the JAK inhibitor era.

PATIENTS AND METHODS

We evaluated patterns of care for older patients with MF before and after ruxolitinib approval, using the Surveillance, Epidemiology, and End Results-Medicare database. Treatment patterns were assessed using Medicare part B and D claims.

RESULTS

This study included 528 patients diagnosed during 2007 to 2015, with a median age at diagnosis of 76 years. Among 298 patients diagnosed in the ruxolitinib era (2012-2015), 113 (37.9%) were ruxolitinib users. Similar numbers of users started ruxolitinib at 5, 10, 15, or 20 milligrams twice a day (BID). Among 31 patients starting at 5 milligrams BID or less, 48.4% were unable to escalate the dose, and < 11 users could increase the dose to the maximum 25 mg BID. Approximately one-half of ruxolitinib users took hydroxyurea and/or prednisone simultaneously with ruxolitinib. The median time on ruxolitinib was 11.9 months (interquartile range, 4.2-21.7 months).

CONCLUSION

It would be important to optimize the use of ruxolitinib and develop new drugs that may be administered together with or after ruxolitinib to accomplish better outcomes in older patients with MF.

The safety of JAK kinase inhibitors for the treatment of myelofibrosis

INTRODUCTION

During the last decade, the development of small molecule inhibitors of Janus kinases (JAKi) contributed to revolutionize the therapeutic landscape of myelofibrosis (MF). JAKi proved to be effective in controlling disease-related symptoms and splenomegaly with remarkable inter-drug variability. However, in some cases the border between clinical efficacy of JAKi and dose-dependent toxicities is narrow leading to sub-optimal dose modifications and/or treatment discontinuation.

AREAS COVERED

In the current review, the authors aimed at providing a comprehensive review of the safety profile of JAKi that are currently approved or in advanced clinical development. Also, a short discussion of promising JAKi in early clinical evaluation and molecules 'lost' early in clinical development is provided. Finally, we discuss the possible strategies aimed at strengthening the safety of JAKi while improving the therapeutic efficacy.

EXPERT OPINION

Overall, JAKi display a satisfactory risk-benefit ratio, with main toxicities being gastrointestinal or related to the myelo/immunosuppressive effects, generally mild and easily manageable. However, JAKi may be associated with potentially life-threatening toxicities, such as neurological and infectious events. Thus, many efforts are needed in order to optimize JAKi-based therapeutic strategies without burdening patient safety. This could be attempted through drug combinations or the development of more selective molecules.

Determining the recommended dose of pacritinib: results from the PAC203 dose-finding trial in advanced myelofibrosis

PAC203 is a randomized dose-finding study of pacritinib, an oral JAK2/IRAK1 inhibitor, in patients with advanced myelofibrosis who are intolerant of or resistant to ruxolitinib. Patients were randomized 1:1:1 to pacritinib 100 mg once per day, 100 mg twice per day, or 200 mg twice per day. Enhanced eligibility criteria, monitoring, and dose modifications were implemented to mitigate risk of cardiac and hemorrhagic events. Efficacy was based on ≥35% spleen volume response (SVR) and ≥50% reduction in the 7-component total symptom score (TSS) through week 24. Of 161 patients, 73% were intolerant of and 76% had become resistant to ruxolitinib; 50% met criteria for both. Severe thrombocytopenia (platelet count <50 × 103/μL) was present in 44%. SVR rates were highest with 200 mg twice per day (100 mg once per day, 0%; 100 mg twice per day, 1.8%; 200 mg twice per day, 9.3%), particularly among patients with baseline platelet counts <50 × 103/μL (17%; 4 of 24). Although TSS response rate was similar across doses (100 mg once per day, 7.7%; 100 mg twice per day, 7.3%; 200 mg twice per day, 7.4%), median percent reduction in TSS suggested a dose-response relationship (-3%, -16%, and -27%, respectively). Pharmacokinetic and pharmacodynamic modeling based on all available data showed greatest SVR and TSS reduction at 200 mg twice per day compared with lower doses. Common adverse events were gastrointestinal events, thrombocytopenia, and anemia. There was no excess of grade ≥3 hemorrhagic or cardiac events at 200 mg twice per day. Pacritinib 200 mg twice per day demonstrated clinical activity and an acceptable safety profile and was selected as the recommended dose for a pivotal phase 3 study in patients with myelofibrosis and severe thrombocytopenia. This trial was registered at www.clinicaltrials.gov as #NCT03165734.

JAK Inhibition for the Treatment of Myelofibrosis: Limitations and Future Perspectives

The 2011 approval of ruxolitinib ushered in the Janus kinase (JAK) inhibitor era in the treatment of myelofibrosis (MF), and 2019 saw the US approval of fedratinib. The first therapeutic agents approved by regulatory authorities for MF, these drugs attenuate the overactive JAK-signal transducer and activator of transcription (STAT) signaling universally present in these patients, translating into major clinical benefits in terms of spleen shrinkage and symptom improvement. These, in turn, confer a survival advantage on patients with advanced disease, demonstrated in the case of ruxolitinib, for which long-term follow-up data are available. However, JAK inhibitors do not improve cytopenias in most patients, have relatively modest effects on bone marrow fibrosis and driver mutation allele burden, and clinical resistance eventually develops. Furthermore, they do not modify the risk of transformation to blast phase; indeed, their mechanism of action may be more anti-inflammatory than truly disease-modifying. This has spurred interest in rational combinations of JAK inhibitors with other agents that may improve cytopenias and drugs that could potentially modify the natural history of MF. Newer JAK inhibitors that are distinguished from ruxolitinib and fedratinib by their ability to improve anemia (eg, momelotinib) or safety and efficacy in severely thrombocytopenic patients (eg, pacritinib) are in phase 3 clinical trials. There is also interest in developing inhibitors that are highly selective for mutant JAK2, as well as "type II" JAK2 inhibitors. Overall, although current JAK inhibitors have limitations, they will likely continue to form the backbone of MF therapy for the foreseeable future.

Fedratinib in patients with myelofibrosis previously treated with ruxolitinib: An updated analysis of the JAKARTA2 study using stringent criteria for ruxolitinib failure

Fedratinib is an oral, selective Janus kinase 2 (JAK2) inhibitor. The phase II JAKARTA2 study assessed fedratinib in patients with intermediate‐ or high‐risk myelofibrosis (MF) who were resistant or intolerant to prior ruxolitinib per investigator assessment. Patients received fedratinib 400 mg/day in 28‐day cycles. The JAKARTA2 outcomes were initially reported using a last‐observation‐carried forward (LOCF) analysis in a “Per Protocol” population. This updated analysis of JAKARTA2 employs intention‐to‐treat analysis principles without LOCF for all treated patients (ITT Population; N = 97), and for a patient subgroup who met more stringent definitions of prior ruxolitinib failure (Stringent Criteria Cohort; n = 79). Median duration of prior ruxolitinib exposure was 10.7 months. The primary endpoint was spleen volume response rate (SVRR; ≥35% spleen volume decrease from baseline to end of cycle 6 [EOC6]). The SVRR was 31% in the ITT Population and 30% in the Stringent Criteria Cohort. Median duration of spleen volume response was not reached. Symptom response rate (≥50% reduction from baseline to EOC6 in total symptom score [TSS] on the modified Myelofibrosis Symptom Assessment Form [MFSAF]) was 27%. Grade 3‐4 anemia and thrombocytopenia rates were 38% and 22%, respectively. Patients with advanced MF substantially pretreated with ruxolitinib attained robust spleen responses and reduced symptom burden with fedratinib.

Management of myelofibrosis after ruxolitinib failure

Over the last decade, the Janus kinase1/2 (JAK1/2) inhibitor ruxolitinib has emerged as a cornerstone of myelofibrosis (MF) management. Ruxolitinib improves splenomegaly and symptoms regardless of driver mutation status, and confers a survival advantage in patients with intermediate-2/high risk MF. However, cytopenias remain problematic, and evidence for a robust anti-clonal effect is lacking. Furthermore, the median duration of spleen response to ruxolitinib in clinical trials is approximately 3 years, and ruxolitinib does not appear to affect the risk of leukemic transformation. There is no therapy approved specifically for patients whose disease 'progresses' on ruxolitinib, defining which remains challenging. The recent regulatory approval of the JAK2 inihibitor fedratinib partially fulfills this unmet need, but much remains to be done. Other JAK inhibitors and a plethora of novel agents are being studied in the ruxolitinib 'failure' setting, as well as 'add-on' therapies to ruxolitinib in patients having a 'sub-optimal' response.

Management of myelofibrosis after ruxolitinib failure

Myelofibrosis is a BCR-ABL1–negative myeloproliferative neoplasm characterized by anemia, progressive splenomegaly, extramedullary hematopoiesis, bone marrow fibrosis, constitutional symptoms, leukemic progression, and shortened survival. Constitutive activation of the Janus kinase/signal transducers and activators of transcription (JAK-STAT) pathway, and other cellular pathways downstream, leads to myeloproliferation, proinflammatory cytokine expression, and bone marrow remodeling. Transplant is the only curative option for myelofibrosis, but high rates of morbidity and mortality limit eligibility. Several prognostic models have been developed to facilitate treatment decisions. Until the recent approval of fedratinib, a JAK2 inhibitor, ruxolitinib was the only available JAK inhibitor for treatment of intermediate- or high-risk myelofibrosis. Ruxolitinib reduces splenomegaly to some degree in almost all treated patients; however, many patients cannot tolerate ruxolitinib due to dose-dependent drug-related cytopenias, and even patients with a good initial response often develop resistance to ruxolitinib after 2–3 years of therapy. Currently, there is no consensus definition of ruxolitinib failure. Until fedratinib approval, strategies to overcome ruxolitinib resistance or intolerance were mainly different approaches to continued ruxolitinib therapy, including dosing modifications and ruxolitinib rechallenge. Fedratinib and two other JAK2 inhibitors in later stages of clinical development, pacritinib and momelotinib, have been shown to induce clinical responses and improve symptoms in patients previously treated with ruxolitinib. Fedratinib induces robust spleen responses, and pacritinib and momelotinib may have preferential activity in patients with severe cytopenias. Reviewed here are strategies to ameliorate ruxolitinib resistance or intolerance, and outcomes of clinical trials in patients with myelofibrosis receiving second-line JAK inhibitors after ruxolitinib treatment.

Thrombocytopenia in patients with myelofibrosis: management options in the era of JAK inhibitor therapy

Myelofibrosis (MF), either appearing de novo (primary MF, PMF) or after a previous diagnosis of essential thrombocythemia or of polycythemia vera, is a progressive disease burdened by symptomatic splenomegaly, debilitating systemic symptoms, ineffective hematopoiesis, and overall reduced survival. Patients often present worsening cytopenias, including thrombocytopenia, secondary to progression of the disease as well as to cytoreductive treatment. Patients with MF and thrombocytopenia have few therapeutic options and there is limited information regarding the management of disease in these settings. This article reviews current evidence for the management of patients with MF and thrombocytopenia, in the era of JAK inhibitors.

Primary analysis of JUMP, a phase 3b, expanded-access study evaluating the safety and efficacy of ruxolitinib in patients with myelofibrosis, including those with low platelet counts

Ruxolitinib is a potent Janus kinase (JAK) 1/JAK2 inhibitor approved for the treatment of myelofibrosis (MF). Ruxolitinib was assessed in JUMP, a large (N = 2233), phase 3b, expanded-access study in MF in countries without access to ruxolitinib outside a clinical trial, which included patients with low platelet counts (<100 × 10⁹ /l) and patients without splenomegaly - populations that have not been extensively studied. The most common adverse events (AEs) were anaemia and thrombocytopenia, but they rarely led to discontinuation (overall, 5·4%; low-platelet cohort, 12·3%). As expected, rates of worsening thrombocytopenia were higher in the low-platelet cohort (all grades, 73·2% vs. 53·5% overall); rates of anaemia were similar (all grades, 52·9% vs. 59·5%). Non-haematologic AEs, including infections, were mainly grade 1/2. Overall, ruxolitinib led to meaningful reductions in spleen length and symptoms, including in patients with low platelet counts, and symptom improvements in patients without splenomegaly. In this trial, the largest study of ruxolitinib in patients with MF to date, the safety profile was consistent with previous reports, with no new safety concerns identified. This study confirms findings from the COMFORT studies and supports the use of ruxolitinib in patients with platelet counts of 50-100 × 10⁹ /l. (ClinicalTrials.gov identifier NCT01493414).

Ruxolitinib in Myelofibrosis and Baseline Thrombocytopenia in Real Life: Results in Dutch Patients and Review of the Literature

BACKGROUND

Ruxolitinib is an approved treatment for myelofibrosis patients, but data regarding patients with baseline thrombocytopenia are limited. The EXPAND study recently suggested tolerability of ruxolitinib, with a maximum starting dose of 10 mg 2 times a day (BID). However, the small sample size and vigorous follow-up in this trial hamper direct translation of these results to routine practice.

PATIENTS AND METHODS

We report retrospective data on Dutch ruxolitinib-treated myelofibrosis patients, focusing on those with baseline thrombocytopenia. Additionally, we reviewed current literature regarding ruxolitinib treatment in this subgroup.

RESULTS

In our cohort, 12 of 119 patients had a baseline platelet count of < 100 × 10⁹/L. Spleen responses at a mean treatment duration of 25 weeks were documented in 1 of 6 and 15 of 47 patients with and without baseline thrombocytopenia, respectively. Despite a high rate of grade 3 or higher thrombocytopenia in thrombocytopenic versus nonthrombocytopenic patients (42% vs. 15%), no grade 3 or higher hemorrhage was reported. Median doses in thrombocytopenic patients were 15 and 10 mg BID at the start and after 12 weeks of treatment, respectively. Additionally, 238 thrombocytopenic patients were identified in the available literature, of whom 59 were treated in routine practice. Incidences of severe thrombocytopenia reported separately for patients with baseline thrombocytopenia were 30% to 59% (grade 3 or higher) and 4% to 60% (grade 4). Severe bleeding, pooled across our data and evaluable studies, occurred in 2.4%.

CONCLUSION

Ruxolitinib treatment appears to be safe for patients with platelet counts of 50 to 100 × 10⁹/L in real-life practice. We did not find any reason to discourage a starting dose of 10 mg BID in this subgroup.

Cotargeting the JAK/STAT signaling pathway and histone deacetylase by ruxolitinib and vorinostat elicits synergistic effects against myeloproliferative neoplasms

The majority of patients with Philadelphia-negative myeloproliferative neoplasms (MPNs) harbor a gain of function mutation V617F in Janus kinase (JAK) 2. Although JAK2 inhibitors such as ruxolitinib have been shown to be clinically efficacious, the hematological toxicity and eventual drug resistance limit its use as monotherapy. Other gene mutations or dysregulation correlated with the disease phenotype and prognosis have been found to contribute to the complexity and heterogeneity of MPNs, giving rise to an increasing demand for combination therapies. Here, we combine ruxolitinib and the histone deacetylase inhibitor vorinostat as a rational combination strategy for MPNs. We tested the combination of ruxolitinib and vorinostat in cells with the JAK2V617F mutation, such as HEL cells, c-Kit⁺ cells from JAK2V617F transgenic mice and bone marrow mononuclear cells (BMMNCs) from patients with MPN. Our results showed significant synergistic effects of this combination strategy. Cotreatment with ruxolitinib and vorinostat synergistically induced apoptosis, cell cycle arrest and inhibition of the colony-forming capacity of HEL cells by attenuating the JAK/signal transducer and activator of transcription (STAT) and protein kinase-B (AKT) signaling pathways. In particular, cotreatment with ruxolitinib and vorinostat prevented the formation of large colonies of colony-forming unit-granulocyte/erythroid/macrophage/megakaryocytes (CFU-GEMMs) and colony-forming unit-granulocyte/macrophages (CFU-GMs) derived from the BMMNCs of patients with MPN. Taken together, these data provided preclinical evidence that the combination of ruxolitinib and vorinostat is a potential dual-target therapy for patients with MPN.

SOHO State of the Art Updates and Next Questions: Myelofibrosis

The discovery of a mutation in the Janus Kinase 2 gene in 2005 spurred significant progress in the field of myeloproliferative neoplasms. A comprehensive description of genomic factors at play in the malignant clone in myeloproliferative neoplasms, particularly myelofibrosis (MF), have recently led to more precise, personalized prognostic tools. Despite this, understanding of the disease pathogenesis remains relatively limited. We continue to lack a detailed description of the interaction between the hematopoietic stem cell clone, abnormal bone marrow niche cells, and circulating signaling molecules and an understanding of how they cooperate to promote cell proliferation, fibrogenesis, and extramedullary hematopoiesis. Despite our knowledge gaps, recent research in MF has led to promising clinical translation. In this article, we summarize recent insights into MF pathophysiology, progress in the development of novel therapeutics, and opportunities for further advancement of the field.

EXPAND, a dose-finding study of ruxolitinib in patients with myelofibrosis and low platelet counts: 48-week follow-up analysis

EEXPAND (phase Ib, dose-finding study) evaluated the starting dose of ruxolitinib in patients with myelofibrosis with baseline platelet counts of 50-99×10⁹/L. The study consisted of dose-escalation and safety-expansion phases. Based on the baseline platelet counts, patients were assigned to stratum 1 (75-99×10⁹/L) or stratum 2 (50-74×10⁹/L), with the primary objective of determining the maximum safe starting dose (MSSD); key secondary objectives included safety and efficacy. At week 48 data cutoff (stratum 1, n=44; stratum 2, n=25), 24.6% (17 out of 69) of patients were still receiving treatment. The MSSD was established as ruxolitinib 10 mg twice daily in both strata. Thrombocytopenia [grade 4 (stratum 1, n=1; stratum 2, n=2)] was the only reported dose-limiting toxicity (study drug related) at 10 mg twice daily. In the MSSD cohort (stratum 1, n=20; stratum 2, n=18), adverse events (regardless of study drug relationship) led to treatment discontinuation in 15.0% and 33.3% of patients in stratum 1 and stratum 2, respectively, and dose adjustment/interruption in 45.0% and 66.7% of patients in stratum 1 and stratum 2, respectively. Three cases of on-treatment deaths were reported at the MSSD. Spleen response was achieved at week 48 in 33.3% and 30.0% of patients in stratum 1 and stratum 2, respectively. Improvements in the Total Symptom Score were also observed. In this study, ruxolitinib demonstrated acceptable tolerability in both the strata at the MSSD of 10 mg twice daily. (Registered at: clinicaltrials.gov identifier: 01317875).

Novel treatments to tackle myelofibrosis

INTRODUCTION

Despite the dramatic progress made in the treatment of patients with myelofibrosis since the introduction of the JAK1/2 inhibitor ruxolitinib, a therapeutic option that can modify the natural history of the disease and prevent evolution to blast-phase is still lacking. Recent investigational treatments including immunomodulatory drugs and histone deacetylase inhibitors benefit some patients but these effects have proven modest at best. Several novel agents do show promising activity in preclinical studies and early-phase clinical trials. We will illustrate a snapshot view of where the management of myelofibrosis is evolving, in an era of personalized medicine and advanced molecular diagnostics. Areas covered: A literature search using MEDLINE and recent meeting abstracts was performed using the keywords below. It focused on therapies in active phases of development based on their scientific and preclinical rationale with the intent to highlight agents that have novel biological effects. Expert commentary: The most mature advances in treatment of myelofibrosis are the development of second-generation JAK1/2 inhibitors and improvements in expanding access to donors for transplantation. In addition, there are efforts to identify drugs that target pathways other than JAK/STAT signaling that might improve the survival of myelofibrosis patients, and limit the need for stem-cell transplantation.

Evaluation of an alternative ruxolitinib dosing regimen in patients with myelofibrosis: an open-label phase 2 study

BACKGROUND

Ruxolitinib improves splenomegaly and symptoms in patients with intermediate-2 or high-risk myelofibrosis; however, nearly half develop grade 3/4 anemia and/or thrombocytopenia, necessitating dose reductions and/or transfusions. We report findings from an open-label phase 2 study exploring a dose-escalation strategy aimed at preserving clinical benefit while reducing hematological adverse events early in ruxolitinib treatment.

METHODS

Patients with myelofibrosis received ruxolitinib 10 mg twice daily (BID), with incremental increases of 5 mg BID at weeks 12 and 18 for lack of efficacy (maximum, 20 mg BID). Symptom severity was measured using the Myelofibrosis Symptom Assessment Form Total Symptom Score (MFSAF TSS).

RESULTS

Forty-five patients were enrolled, 68.9% of whom had a Dynamic International Prognostic Scoring System score of 1 to 2 (i.e., intermediate-1 disease risk). Median percentage change in spleen volume from baseline to week 24 was - 17.3% (≥ 10% reduction achieved by 26 patients [57.8%]), with a clear dose response. Median percentage change in MFSAF TSS from baseline at week 24 was - 45.6%, also with a dose response. The most frequent treatment-emergent adverse events were anemia (26.7%), fatigue (22.2%), and arthralgias (20.0%). Grade 3/4 anemia (20.0%) and dose decreases due to anemia (11.1%) or thrombocytopenia (6.7%) were infrequent.

CONCLUSIONS

A dose-escalation approach may mitigate worsening anemia during early ruxolitinib therapy in some patients with myelofibrosis.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT01445769 . Registered September 23, 2011.

Ruxolitinib therapy for myelofibrosis in Austria : Consensus on therapy management

The oral Janus associated kinase (JAK1/2) inhibitor ruxolitinib has been available for treatment of patients with intermediate or high-risk myelofibrosis in Europe since 2012. Since its introduction, the expertise of prescribing doctors with respect to ruxolitinib function, efficacy and adverse effects has consistently been augmented, resulting in therapy modalities that are better tailored to individual patients as well as in increased safety of the treatment. The present consensus on ruxolitinib therapy management has been elaborated by Austrian experts in myeloproliferative neoplasms in line with international treatment guidelines. Our recommendations aim to contribute to an improved management of patients with myelofibrosis treated with ruxolitinib.

How I treat myelofibrosis after failure of JAK inhibitors

The introduction of JAK inhibitors, leading to regulatory approval of ruxolitinib, represents a major therapeutic advance in myelofibrosis (MF). Most patients experience reduction in splenomegaly and improved quality of life from symptom improvement. It is a paradox, however, that, despite inhibition of signaling downstream of disease-related driver mutations, JAK inhibitor treatment is not associated with consistent molecular or pathologic responses in MF. Furthermore, there are important limitations to JAK inhibitor therapy including development of dose-limiting cytopenias and/or nonhematological toxicities such as neuropathy or opportunistic infections. Over half of the patients discontinue treatment within 3 years of starting treatment. Although data are sparse, clinical outcome after JAK inhibitor "failure" is likely poor; consequently, it is important to understand patterns of failure to select appropriate salvage treatment(s). An algorithmic approach, particularly one that incorporates cytogenetics/molecular data, is most helpful in selecting stem cell transplant candidates. Treatment of transplant-ineligible patients relies on a problem-based approach that includes use of investigational drugs, or consideration of splenectomy or radiotherapy. Data from early phase ruxolitinib combination studies, despite promising preclinical data, have not shown clear benefit over monotherapy thus far. Development of effective treatment strategies for MF patients failing JAK inhibitors remains a major unmet need.

Recommendations on the use of ruxolitinib for the treatment of myelofibrosis

OBJECTIVES

Myelofibrosis (MF) is a severe disease, with decreased life expectancy and heavy symptom burden. Ruxolitinib is the only approved pharmacotherapy for the treatment of MF patients. In Belgium, ruxolitinib is only reimbursed for MF patients with splenomegaly for whom the disease is categorized as intermediate-2 or high risk. The improvement of symptoms without spleen volume reduction is not considered sufficient to continue treatment. The aim of this manuscript is to provide guidance for the safe and effective administration of ruxolitinib, considering the particularities of the Belgian reimbursement criteria.

METHODS

Our recommendations are based on a consensus reached during two meetings, where available data and observations derived from clinical experience were discussed.

RESULTS AND DISCUSSION

We recommend changing the current Belgian reimbursement conditions to include the evaluation of disease-related symptoms along with splenomegaly to decide whether ruxolitinib treatment should be continued or not. Indeed, the decrease in disease-related symptoms seems to be an equally important parameter as the decrease in splenic volume in the evaluation of the response to ruxolitinib. We also advocate for the treatment with ruxolitinib of MF patients in lower-risk categories with severe disease-related symptoms, as this drug could greatly improve their quality of life. Optimization of the ruxolitinib dose is recommended to avoid an unnecessary decrease in platelet count or hemoglobin that may jeopardize treatment continuation.

CONCLUSION

With the aim to optimize the treatment of MF patients, the Belgian regulation for ruxolitinib should be revised in terms of reimbursement criteria, dose titration, stopping rules, and patient follow-up.

Current approaches to challenging scenarios in myeloproliferative neoplasms

INTRODUCTION

The Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) including polycythemia vera, essential thrombocythemia and primary myelofibrosis are clonal hematological malignancies that originate at the level of the hematopoietic stem cell, and are characterized by excessive proliferation of cells belonging to one or more of the myeloid lineages. Central to the pathogenesis of the MPNs is constitutive activation of the JAK/STAT signaling pathway due to a family of driver mutations affecting JAK2, CALR or MPL. These disorders share common clinical and laboratory features, a significant burden of systemic symptoms, increased risk of developing arterial and venous thrombotic events, and the potential to progress to myelofibrosis and acute leukemia. Areas covered: We identified four clinical situations which represent challenging management dilemmas for patients with MPNs. Our conclusions and recommendations are based on a literature search using MEDLINE and recent meeting abstracts using the keywords, focusing on publications directly addressing these scenarios and on recent contributions to the field. Expert commentary: Multi-center efforts to study large cohorts of MPN patients have led to more uniform and evidence-based approaches to key aspects in MPN management. However, treatment strategies to deal with specific clinical scenarios are lacking.

Significance of thrombocytopenia in patients with primary and postessential thrombocythemia/polycythemia vera myelofibrosis

Severe thrombocytopenia (platelets <50 × 10⁹ /L) is associated with very poor outcome of patients with myelofibrosis (MF). As patients with primary myelofibrosis (PMF) differ from patients with postessential thrombocythemia (PET-MF) and postpolycythemia vera myelofibrosis (PPV-MF), we aimed to evaluate the significance of low platelets among these patients. We present clinical characteristics and outcome of patients with either PMF, PPV-MF, or PET-MF, and thrombocytopenia who presented to our institution between 1984 and 2015. Of 1269 patients (877 PMF, 212 PPV-MF, 180 PET-MF), 11% and 14% had platelets either <50 × 10⁹ /L or between 50-100 × 10⁹ /L, respectively. Patients with platelets <50 × 10⁹ /L were most anemic and transfusion dependent, had highest blast count and unfavorable karyotype. In general, their overall and leukemia-free survival was the shortest with median time of 15 and 13 months, respectively; with incidence of acute leukemia almost twice as high as in the remaining patients (6.9 vs 3.6 cases per 100 person-years). Nevertheless, this observation remains mostly significant for patients with PMF, as those with PEV/PVT-MF have already significantly inferior prognosis with platelets <100 × 10⁹ /L.

Ruxolitinib

Ruxolitinib, formerly known as INCB018424 or INC424, is a potent and selective oral inhibitor of Janus kinase (JAK) 1 and JAK2. Ruxolitinib has been approved for the treatment of myelofibrosis (MF) by the US Food and Drug Administration (FDA) in 2011 and by the European Medicines Agency (EMA) in 2012, followed by the approval for the treatment of hydroxyurea (HU)-resistant or -intolerant polycythemia vera (PV) in 2014. Both MF and PV are myeloproliferative neoplasms (MPNs) which are characterized by the aberrant activation of the JAK-STAT pathway. Clinically, MF features bone marrow fibrosis, splenomegaly, abnormal blood counts, and poor quality-of-life through associated symptoms. PV is characterized by the overproduction of primarily red blood cells (RBC), risk of thrombotic complications, and development of secondary MF. Ruxolitinib treatment results in a meaningful reduction in spleen size and symptom burden in the majority of MF patients and may also have a favorable effect on survival. In PV, ruxolitinib effectively controls the hematocrit and reduces splenomegaly. Since recently, ruxolitinib is also under investigation for the treatment of graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (HSCT). Toxicities of ruxolitinib include myelosuppression, which results in dose-limiting thrombocytopenia and anemia, and viral reactivations. The metabolization of ruxolitinib through CYP3A4 needs to be considered particularly if co-administered with potent CYP3A4 inhibitors. Several further JAK inhibitors are currently under investigation for MPNs or other immuno-inflammatory diseases.

Emerging therapies for atopic dermatitis: JAK inhibitors

The Janus kinase-signal transducer and activator of transcription pathway is a conserved master regulator of immunity and myeloproliferation. Advanced understanding of this pathway has led to development of targeted inhibitors of Janus kinases (Jakinibs). As a class, JAK inhibitors effectively treat a multitude of hematologic and inflammatory diseases. Given such success, use of JAK inhibitors for mitigation of atopic dermatitis is under active investigation. Herein, we review the evolving data on the safety and efficacy of JAK inhibitors in treatment of atopic dermatitis. Although it is still early in the study of JAK inhibitors for atopic dermatitis, evidence identifies JAK inhibitors as effective alternatives to conventional therapies. Nonetheless, multiple large safety and efficacy trials are needed before widespread use of JAK inhibitors can be advocated for atopic dermatitis.

Novel Therapies for Myelofibrosis

PURPOSE OF REVIEW

The purpose of the review was to provide a contemporary update of novel agents and targets under investigation in myelofibrosis in the Janus kinase (JAK) inhibitor era.

RECENT FINDINGS

Myelofibrosis (MF) is a clonal stem cell disease characterized by marrow fibrosis and a heterogeneous disease phenotype with a variable degree of splenomegaly, cytopenias, and constitutional symptoms that significantly impact quality of life and survival. Overactive JAK/STAT signaling is a hallmark of MF. The only approved therapy for MF, JAK1/2 inhibitor ruxolitinib, can ameliorate splenomegaly, improve symptoms, and prolong survival in some patients. Therapeutic challenges remain, however. Myelosuppression limits the use of ruxolitinib in some patients, eventual drug resistance is common, and the underlying malignant clone persists despite therapy. A deeper understanding of the pathogenesis of MF has informed the development of additional agents. Promising targets under investigation include JAK1 and JAK2 and downstream intermediates in related signaling pathways, epigenetic modifiers, pro-inflammatory cytokines, and immune regulators.

An updated review of the JAK1/2 inhibitor (ruxolitinib) in the Philadelphia-negative myeloproliferative neoplasms

Ruxolitinib (Rux), a JAK1/2 inhibitor, has been approved for patients with myelofibrosis and in polycythemia vera with inadequate response/intolerance to hydroxycarbamide. Studies have demonstrated that Rux improves disease-related symptoms and splenomegaly. A late emerging observation from two Phase III trials was that Rux was associated with survival advantage in comparison with placebo or other available therapies in myelofibrosis. Important data suggest that for polycythemia vera Rux improved control of blood counts. Main hematological side effects are anemia and thrombocytopenia predominantly at the beginning of the treatment. Some studies and case reports highlighted potential risks of nonmelanoma skin cancers and increased risk of infection including reactivation of hepatitis B, tuberculosis or herpes zoster infections after Rux treatment.

Symptom burden profile in myelofibrosis patients with thrombocytopenia: Lessons and unmet needs

Myelofibrosis is a myeloproliferative neoplasm associated with progressive cytopenias and high symptom burden. MF patients with thrombocytopenia have poor prognosis but the presence of thrombocytopenia frequently precludes the use of JAK2 inhibitors. In this study, we assessed quality of life and symptom burden in 418 MF patients with (n=89) and without (n=329) thrombocytopenia using prospective data from the MPN-QOL study group database, including the Myeloproliferative Neoplasm Symptom Assessment Form (MPN-SAF) and Total Symptom Score (MPN10). Thrombocytopenia, defined as platelet count <100×10⁹/L (moderate 51-100×10⁹/L; severe ≤50×10⁹/L), was associated with anemia (76% vs. 45%, p<0.001), leukopenia (29% vs. 11%, p<0.001), and need for red blood cell transfusion (35% vs. 19%, p=0.002). Thrombocytopenic patients had more fatigue, early satiety, inactivity, dizziness, sad mood, cough, night sweats, itching, fever, and weight loss; total symptom scores were also higher (33 vs. 24, p<0.001). Patients with severe thrombocytopenia were more likely to have anemia (86% vs. 67%, p=0.04), leukopenia (40% vs. 20%, p=0.04), and transfusion requirements (51% vs. 20%, p=0.002) but few differences in symptoms when compared to patients with moderate thrombocytopenia. These results suggest that MF patients with thrombocytopenia experience greater symptomatic burden than MF patients without thrombocytopenia and may benefit from additional therapies.

Managing side effects of JAK inhibitors for myelofibrosis in clinical practice

INTRODUCTION

Myelofibrosis (MF) is characterized by bone marrow fibrosis, abnormalities in peripheral counts, extramedullary hematopoiesis, splenomegaly and an increased risk of transformation to acute myeloid leukaemia. The disease course is often heterogeneous and management can range from observation alone through to allogeneic stem cell transplantation. As of 2017, the only approved medication for MF remains the JAK Inhibitor (JAKi), ruxolitinib (Novartis Pharmaceuticals, Basel, Switzerland; Incyte, Wilmington, Detroit, USA) although several others have reached advanced stages of clinical trials. Areas covered: In this review, we focus on the management of both common and uncommon side effects arising from the use of currently approved and clinical trial JAKi. Most of the discussion concerns ruxolitinib although we also cover both pacritinib (CTI BioPharma) and momelotinib (Gilead Sciences, Foster City, California) which have been in recent large, multinational phase III trials. The various approaches to management of JAKi-related side effects are discussed - with particular emphasis to anaemia, thrombocytopaenia and infection risk. Expert commentary: JAK inhibitors are effective in many individuals with MF and have revolutionized the current treatment paradigm. The side effect profile, in the most, is predictable and manageable with high degrees of clinical surveillance and dose modifications.

Pacritinib versus best available therapy for the treatment of myelofibrosis irrespective of baseline cytopenias (PERSIST-1): an international, randomised, phase 3 trial

BACKGROUND

Available therapies for myelofibrosis can exacerbate cytopenias and are not indicated for patients with severe thrombocytopenia. Pacritinib, which inhibits both JAK2 and FLT3, induced spleen responses with limited myelosuppression in phase 1/2 trials. We aimed to assess the efficacy and safety of pacritinib versus best available therapy in patients with myelofibrosis irrespective of baseline cytopenias.

METHODS

This international, multicentre, randomised, phase 3 trial (PERSIST-1) was done at 67 sites in 12 countries. Patients with higher-risk myelofibrosis (with no exclusions for baseline anaemia or thrombocytopenia) were randomly assigned (2:1) to receive oral pacritinib 400 mg once daily or best available therapy (BAT) excluding JAK2 inhibitors until disease progression or unacceptable toxicity. Randomisation was stratified by risk category, platelet count, and region. Treatment assignments were known to investigators, site personnel, patients, clinical monitors, and pharmacovigilance personnel. The primary endpoint was spleen volume reduction (SVR) of 35% or more from baseline to week 24 in the intention-to-treat population as assessed by blinded, centrally reviewed MRI or CT. We did safety analyses in all randomised patients who received either treatment. Here we present the final data. This trial is registered with ClinicalTrials.gov, number NCT01773187.

FINDINGS

Between Jan 8, 2013, and Aug 1, 2014, 327 patients were randomly assigned to pacritinib (n=220) or BAT (n=107). Median follow-up was 23·2 months (IQR 14·8-28·7). At week 24, the primary endpoint of SVR of 35% or more was achieved by 42 (19%) patients in the pacritinib group versus five (5%) patients in the BAT group (p=0·0003). 90 patients in the BAT group crossed over to receive pacritinib at a median of 6·3 months (IQR 5·8-6·7). The most common grade 3-4 adverse events through week 24 were anaemia (n=37 [17%]), thrombocytopenia (n=26 [12%]), and diarrhoea (n=11 [5%]) in the pacritinib group, and anaemia (n=16 [15%]), thrombocytopenia (n=12 [11%]), dyspnoea (n=3 [3%]), and hypotension (n=3 [3%]) in the BAT group. The most common serious adverse events that occurred through week 24 were anaemia (10 [5%]), cardiac failure (5 [2%]), pyrexia (4 [2%]), and pneumonia (4 [2%]) with pacritinib, and anaemia (5 [5%]), sepsis (2 [2%]), and dyspnoea (2 [2%]) with BAT. Deaths due to adverse events were observed in 27 (12%) patients in the pacritinib group and 14 (13%) patients in the BAT group throughout the duration of the study.

INTERPRETATION

Pacritinib therapy was well tolerated and induced significant and sustained SVR and symptom reduction, even in patients with severe baseline cytopenias. Pacritinib could be a treatment option for patients with myelofibrosis, including those with baseline cytopenias for whom options are particularly limited.

FUNDING

CTI BioPharma Corp.

Ruxolitinib in myelofibrosis: to be or not to be an immune disruptor

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm classified according to the 2016 revision of World Health Organization Classification of Tumors and Haematopoietic and Lymphoid Tissue. Ruxolitinib is an oral inhibitor of Janus kinase approved in the USA for the treatment of intermediate or high-risk PMF and approved in Europe for the treatment of splenomegaly and constitutional symptoms of the disease. More recently, case reports described serious opportunistic infections in this neoplasm treated with ruxolitinib. Research studies demonstrated the immunological derangement of this compound mainly based on T, dendritic, and natural killer cell defects. The purpose of this review of the literature was to analyze the relationship among ruxolitinib, immune system and bacterial, viral, fungal, and protozoan infections. A literature search was conducted using PubMed articles published between January 2010 and November 2016. The efficacy of drug in patients with PMF was demonstrated in two phase III studies, Controlled MyeloFibrosis Study with ORal Jak inhibitor Treatment (COMFORT-I and COMFORT-II). Grade 3 and 4 neutropenia were recognized in 7.1% and 2% of patients in the ruxolitinib and placebo arm of COMFORT-I. Grade 3 or 4 neutropenia or leukopenia were observed in 8.9% and 6.3% of ruxolitinib treated patients of 5-year follow-up of COMFORT-II. In addition, leukocyte subpopulations, lymphocyte functions, or antibody deficiency were not documented in either of the studies. The complex interactions between ruxolitinib, bone marrow, immune system, and infections in PMF need further investigation, robust data from a randomized clinical trial, registry, or large case-series.

A Review of Ruxolitinib for the Treatment of Myelofibrosis: A Critique of the Evidence

As part of the National Institute for Health and Care Excellence's (NICE) Single Technology Appraisal (STA) process, ruxolitinib was assessed to determine the clinical and cost effectiveness of its use in the treatment of disease-related splenomegaly or symptoms in adults with myelofibrosis. Ruxolitinib had previously been assessed as part of the STA process and was not recommended in NICE guidance issued in June 2013 (TA289). A review of TA289 was commissioned following the availability of new longer-term survival data; a price discount patient access scheme (PAS) was also introduced. The Centre for Reviews and Dissemination (CRD) and Centre for Health Economics (CHE) Technology Appraisal Group at the University of York was commissioned to act as the independent Evidence Review Group (ERG). This article provides a summary of the manufacturer or sponsor of the technology's (referred to as the company) submission, the ERG review and the resulting NICE guidance issued in March 2016. The main clinical effectiveness data were derived from two good-quality multicentre randomised controlled trials (RCTs): COMFORT-II compared ruxolitinib with best available therapy (BAT) and COMFORT-I compared ruxolitinib with placebo. Both RCTs demonstrated a statistically significant reduction in splenomegaly and its associated symptoms in intermediate-2 and high-risk myelofibrosis patients. Overall survival was statistically significantly improved with ruxolitinib compared with BAT at 3.5 years of follow-up in the COMFORT-II trial (hazard ratio 0.58, 95 % CI 0.36-0.93). Grade 3-4 adverse events were more frequent in the ruxolitinib group than in the BAT group; 42 % compared with 25 %. Evidence relating to patients with lower-risk disease or low platelet counts (50-100 × 10⁹/L) was less robust. The company's economic model was well-presented and had an appropriate model structure. The base-case incremental cost-effectiveness ratio (ICER) was estimated to be around £45,000 per quality-adjusted life-year (QALY) gained (including the PAS discount). Extensive sensitivity and scenario analyses were presented, demonstrating that the estimated ICER was robust to a range of input values and assumptions made in the model. Alternative scenarios presented by the ERG showed only modest increases in the estimated ICER, primarily as a result of including an element of drug wastage within the model. Alternative scenarios resulted in estimated ICERs ranging from around £45,000 to £49,000 per QALY gained (including the PAS discount). At the first appraisal meeting, the NICE Appraisal Committee concluded that ruxolitinib was clinically effective and was a cost effective use of National Health Service (NHS) resources for patients with high-risk myelofibrosis who meet NICE's end-of-life criteria. Following the consultation, the company offered a revised PAS, resulting in a revised base-case ICER of £31,229 per QALY gained. The company also presented new evidence on the cost effectiveness of ruxolitinib in intermediate-2 and high-risk subgroups and a revised version of the model. The NICE Appraisal Committee considered the new evidence and recommended ruxolitinib for the treatment of patients with intermediate-2-risk disease as well as patients with high-risk disease, based on International Prognostic Scoring System (IPSS) prognostic factors.

The Amelioration of Myelofibrosis with Thrombocytopenia by a JAK1/2 Inhibitor, Ruxolitinib, in a Post-polycythemia Vera Myelofibrosis Patient with a JAK2 Exon 12 Mutation

Less than 5% of patients with polycythemia vera (PV) show JAK2 exon 12 mutations. Although PV patients with JAK2 exon 12 mutations are known to develop post-PV myelofibrosis (MF) as well as PV with JAK2V617F, the role of JAK inhibitors in post-PV MF patients with JAK2 exon 12 mutations remains unknown. We describe how treatment with a JAK1/2 inhibitor, ruxolitinib, led to the rapid amelioration of marrow fibrosis, erythrocytosis and thrombocytopenia in a 77-year-old man with post-PV MF who carried a JAK2 exon 12 mutation (JAK2H538QK539L). This case suggests that ruxolitinib is a treatment option for post-PV MF in patients with thrombocytopenia or JAK2 exon 12 mutations.

Austrian recommendations for the management of primary myelofibrosis, post-polycythemia vera myelofibrosis and post-essential thrombocythemia myelofibrosis: an expert statement

The entity "myelofibrosis" represents a subgroup of the Philadelphia chromosome-negative myeloproliferative neoplasms. It comprises primary myelofibrosis, post-polycythemia vera myelofibrosis and post-essential thrombocythemia myelofibrosis. This heterogeneous disease is characterized by clonal myeloproliferation, dysregulated kinase signalling and the abnormal expression of several proinflammatory cytokines. Clinically, patients present with symptoms related to thrombocytosis/leukocytosis, anemia and/or progressive splenomegaly. Mutations in Janus kinase 2, an enzyme that is essential for the normal development of erythrocytes, granulocytes, and platelets, notably the V617F mutation, have been identified in approximately 60% of patients with primary myelofibrosis. Recent molecular advances have not only elucidated critical pathways in the pathogenesis of the disease, but also contributed to a more precise assessment of a patient's individual risk. While allogeneic stem cell transplantation remains the only curative treatment, the natural course of the disease and the patient's survival and quality of life may be improved by new treatments, notably ruxolitinib, the first Janus kinase 1/2 inhibitor approved for the management of myelofibrosis. Additional treatment options are being explored.