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

Recent progress of JAK inhibitors for hematological disorders

JAK inhibitors are important therapeutic options for hematological disorders, especially myeloproliferative neoplasms. Ruxolitinib, the first JAK inhibitor approved for clinical use, improves splenomegaly and ameliorates constitutional symptoms in both myelofibrosis and polycythemia vera patients. Ruxolitinib is also useful for controlling hematocrit levels in polycythemia vera patients who were inadequately controlled by conventional therapies. Furthermore, pretransplantation use of ruxolitinib may improve the outcome of allo-hematopoietic stem cell transplantation in myelofibrosis. In contrast to these clinical merits, evidence of the disease-modifying action of ruxolitinib, i.e., reduction of malignant clones or improvement of bone marrow pathological findings, is limited, and many myelofibrosis patients discontinued ruxolitinib due to adverse events or disease progression. To overcome these limitations of ruxolitinib, several new types of JAK inhibitors have been developed. Among them, fedratinib was proven to provide clinical merits even in patients who were resistant or intolerant to ruxolitinib. Pacritinib and momelotinib have shown merits for myelofibrosis patients with thrombocytopenia or anemia, respectively. In addition to treatment for myeloproliferative neoplasms, recent studies have demonstrated that JAK inhibitors are novel and attractive therapeutic options for corticosteroid-refractory acute as well as chronic graft versus host disease.

Ruxolitinib withdrawal complicating emergency aortic root replacement

Ruxolitinib, a Janus kinase inhibitor, is associated with severe withdrawal phenomena. Adequate tapering is often underemphasized in surgical emergencies and can complicate the postoperative course. We present a case of acute ruxolitinib withdrawal in a gentleman undergoing emergency cardiac surgery

Light and shade of ruxolitinib: positive role of early treatment with ruxolitinib and ruxolitinib withdrawal syndrome in patients with myelofibrosis

INTRODUCTION

Myelofibrosis (MF) is characterized by ineffective and hepatosplenic extramedullary hematopoiesis due to fibrotic changes in the bone marrow and systemic manifestations due to aberrant cytokine release. Ruxolitinib (RUX) is the first JAK1/JAK2 inhibitor that is clinically approved to treat splenomegaly by ameliorating inflammatory cytokines and myeloproliferation in MF.

AREAS COVERED

Patients with less advanced MF may also achieve better outcome and successful treatment with RUX. However, approximately 40% of the patients failed to achieve a stable response or have shown to be intolerant to RUX, and most of them discontinued RUX. In patients who need to discontinue or reduce the dose of RUX for any reason, RUX is known to induce a paradoxical accumulation of JAK activation loop phosphorylation that is causing RUX discontinuation syndrome (RDS). To review the topic of MF and RUX, we searched relevant literatures using PubMed.

EXPERT OPINION

RUX treatment in lower IPSS risk patients who present with splenomegaly and disease-associated symptoms can be helpful. A careful discontinuation strategy with steroids may reduce the probability of RDS, and the recognition of RDS with early re-introduction of RUX is important in the treatment of severe cases of RDS.

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.

Emerging Place of JAK Inhibitors in the Treatment of Inborn Errors of Immunity

Among inborn errors of immunity (IEIs), some conditions are characterized by inflammation and autoimmunity at the front line and are particularly challenging to treat. Monogenic diseases associated with gain-of-function mutations in genes critical for cytokine signaling through the JAK-STAT pathway belong to this group. These conditions represent good candidates for treatment with JAK inhibitors. Type I interferonopathies, a group of recently identified monogenic auto-inflammatory diseases characterized by excessive secretion of type I IFN, are also good candidates with growing experiences reported in the literature. However, many questions remain regarding the choice of the drug, the dose (in particular in children), the efficacy on the various manifestations, the monitoring of the treatment, and the management of potent side effects in particular in patients with infectious susceptibility. This review will summarize the current experiences reported and will highlight the unmet needs.

Hypoxemic Respiratory Failure Following Ruxolitinib Discontinuation in Allogeneic Hematopoietic Cell Transplantation Recipients

Ruxolitinib, a selective inhibitor of Janus kinases 1 and 2, is increasingly being used in allogeneic hematopoietic cell transplantation (HCT) recipients following its approval by the U.S. Food and Drug Administration for the treatment of steroid-refractory acute graft-versus-host disease. Although there is extensive experience using ruxolitinib for patients with myeloproliferative neoplasms, the biologic effects and clinical implications of its dosing, tapering, and discontinuation for allogeneic HCT recipients are incompletely characterized. We describe three allogeneic HCT recipients who developed acute hypoxemic respiratory failure within 3 months of ruxolitinib discontinuation. Radiographic findings included marked bilateral ground-glass opacities. Systemic corticosteroids and reinitiation of ruxolitinib resulted in rapid clinical improvement in all three patients. All three patients achieved a significant clinical response, with decrease in oxygen requirement and improvement in radiographic changes. Given the increasing use of ruxolitinib in allogeneic HCT recipients, there is significant impetus to characterize the biologic and clinical effects resulting from discontinuation of ruxolitinib, to better tailor treatment plans and prevent potential adverse effects.

Persistence of myelofibrosis treated with ruxolitinib: biology and clinical implications

Activation of JAK-STAT signaling is one of the hallmarks of myelofibrosis, a myeloproliferative neoplasm that leads to inflammation, progressive bone marrow failure, and a risk of leukemic transformation. Around 90% of patients with myelofibrosis have a mutation in JAK2, MPL, or CALR: so-called 'driver' mutations that lead to activation of JAK2. Ruxolitinib, and other JAK2 inhibitors in clinical use, provide clinical benefit but do not have a major impact on the abnormal hematopoietic clone. This phenomenon is termed 'persistence', in contrast to usual patterns of resistance. Multiple groups have shown that type 1 inhibitors of JAK2, which bind the active conformation of the enzyme, lead to JAK2 becoming resistant to degradation with consequent accumulation of phospho-JAK2. In turn, this can lead to exacerbation of inflammatory manifestations when the JAK inhibitor is discontinued, and it may also contribute to disease persistence. The ways in which JAK2 V617F and CALR mutations lead to activation of JAK-STAT signaling are incompletely understood. We summarize what is known about pathological JAK-STAT activation in myelofibrosis and how this might lead to future novel therapies for myelofibrosis with greater disease-modifying potential.

Ruxolitinib rechallenge in resistant or intolerant patients with myelofibrosis: Frequency, therapeutic effects, and impact on outcome

BACKGROUND

After ruxolitinib discontinuation, the outcome of patients with myelofibrosis (MF) is poor with scarce therapeutic possibilities.

METHODS

The authors performed a subanalysis of an observational, retrospective study (RUX-MF) that included 703 MF patients treated with ruxolitinib to investigate 1) the frequency and reasons for ruxolitinib rechallenge, 2) its therapeutic effects, and 3) its impact on overall survival.

RESULTS

A total of 219 patients (31.2%) discontinued ruxolitinib for ≥14 days and survived for ≥30 days. In 60 patients (27.4%), ruxolitinib was rechallenged for ≥14 days (RUX-again patients), whereas 159 patients (72.6%) discontinued it permanently (RUX-stop patients). The baseline characteristics of the 2 cohorts were comparable, but discontinuation due to a lack/loss of spleen response was lower in RUX-again patients (P = .004). In comparison with the disease status at the first ruxolitinib stop, at its restart, there was a significant increase in patients with large splenomegaly (P < .001) and a high Total Symptom Score (TSS; P < .001). During the rechallenge, 44.6% and 48.3% of the patients had spleen and symptom improvements, respectively, with a significant increase in the number of patients with a TSS reduction (P = .01). Although the use of a ruxolitinib dose > 10 mg twice daily predicted better spleen (P = .05) and symptom improvements (P = .02), the reasons for/duration of ruxolitinib discontinuation and the use of other therapies before rechallenge were not associated with rechallenge efficacy. At 1 and 2 years, 33.3% and 48.3% of RUX-again patients, respectively, had permanently discontinued ruxolitinib. The median overall survival was 27.9 months, and it was significantly longer for RUX-again patients (P = .004).

CONCLUSIONS

Ruxolitinib rechallenge was mainly used in intolerant patients; there were clinical improvements and a possible survival advantage in many cases, but there was a substantial rate of permanent discontinuation. Ruxolitinib rechallenge should be balanced against newer therapeutic possibilities.

Ruxolitinib before allogeneic hematopoietic transplantation in patients with myelofibrosis on behalf SFGM-TC and FIM groups

This multicenter prospective phase 2 trial analyzed disease-free survival (DFS) in myelofibrosis patients receiving ruxolitinib for 6 months before transplantation. Seventy-six patients were recruited. Age-adjusted dynamic international prognostic scoring system was intermediate-1, intermediate-2, and high in 27 (36%), 31 (41%), and 18 (24%) patients. All patients received ruxolitinib from inclusion to conditioning regimen (fludarabine-melphalan) or to progression. A donor was found in 64 patients: 18 HLA-matched sibling donor (MSD), 32 HLA-matched unrelated (UD10/10), and 14 HLA mismatched unrelated donor (UD9/10. Among 64 patients with a donor, 20 (31%) achieved a partial response before transplantation and 59 (92%) could be transplanted after ruxolitinib therapy (18/18 MSD, 30/21 UD10/10, 11/34 UD9/10), of whom 19 (32%) were splenectomized. Overall survival from inclusion was 68% at 12 months. One-year DFS after transplantation was 55%: 83%, 40%, and 34% after MSD, UD10/10 or UD9/10, respectively. Cumulative incidence of grade 2–4 acute graft-versus-host disease (GVHD) was 66% and non-relapse-mortality was 42% at 12 months. Short course of ruxolitinib before transplantation is followed by a high rate of transplantation. With the platform used in this protocol, outcome was much better in patients transplanted with HLA-matched sibling donor as compared to unrelated donor.

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.

The Janus kinase 1/2 inhibitor ruxolitinib in COVID-19 with severe systemic hyperinflammation

A subgroup of patients with severe COVID-19 suffers from progression to acute respiratory distress syndrome and multiorgan failure. These patients present with progressive hyperinflammation governed by proinflammatory cytokines. An interdisciplinary COVID-19 work flow was established to detect patients with imminent or full blown hyperinflammation. Using a newly developed COVID-19 Inflammation Score (CIS), patients were prospectively stratified for targeted inhibition of cytokine signalling by the Janus Kinase 1/2 inhibitor ruxolitinib (Rux). Patients were treated with efficacy/toxicity guided step up dosing up to 14 days. Retrospective analysis of CIS reduction and clinical outcome was performed. Out of 105 patients treated between March 30th and April 15th, 2020, 14 patients with a CIS ≥ 10 out of 16 points received Rux over a median of 9 days with a median cumulative dose of 135 mg. A total of 12/14 patients achieved significant reduction of CIS by ≥25% on day 7 with sustained clinical improvement in 11/14 patients without short term red flag warnings of Rux-induced toxicity. Rux treatment for COVID-19 in patients with hyperinflammation is shown to be safe with signals of efficacy in this pilot case series for CRS-intervention to prevent or overcome multiorgan failure. A multicenter phase-II clinical trial has been initiated (NCT04338958).

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.

Cancer Treatment-Related Lung Injury

Lung injury associated with cancer therapeutics is often the limiting factor that trumps otherwise successful cancer therapy. Thoracic radiation as well as cancer pharmacotherapeutics, including conventional chemotherapy, molecular targeted agents, and cancer immunotherapies, have been associated with a unique spectrum of histopathologic injury patterns that may involve the lung parenchyma, pleura, airways, and/or pulmonary vasculature. Injury patterns may be idiosyncratic, unpredictable, and highly variable from one agent class to the next. Variability in lung injury patterns within a specific therapeutic class of drugs also occurs, adding to the conundrum. Drug-induced toxicities to the thoracic cavity are infrequent, and early recognition of clinical clues portends a good outcome in most cases. Failure to recognize early clinical signs, however, may result in irreversible and potentially lethal consequences.

This chapter provides an overview of our current knowledge of thoracic complications associated with cancer pharmacotherapies. The review is not intended to be a treatise of all cancer agents that adversely affect the lungs, but rather a discussion of established risk factors and histopathologic patterns of lung injury associated with broad classes of cancer agents. Optimal management strategies, based on existing clinical experience, will also be discussed. Complications associated with thoracic radiation are also reviewed. It is hoped that these discussions will facilitate early recognition and management of treatment-related thoracic complications and, ultimately, better patient outcomes.

Rapid disease progression following discontinuation of ibrutinib in patients with chronic lymphocytic leukemia treated in routine clinical practice

We identified all patients with chronic lymphocytic leukemia at Mayo Clinic treated with ibrutinib outside the context of a clinical trial; timing and reasons for discontinuation were ascertained, as were symptoms, exam and radiographic findings, and laboratory changes following discontinuation. Of 202 patients who received ibrutinib, 52 discontinued therapy (estimated 1- and 2-year risk of discontinuation 18% and 28%, respectively). The most common reasons for discontinuation were toxicity (56%) and progression of disease (32%, including Richter's transformation in 15%). Rapid progression of disease within 4 weeks after discontinuation was observed in 9/36 (25%) patients with adequate records for review, mostly in those stopping ibrutinib for disease progression (n = 8) rather than toxicity (n = 1). This was evident by sudden worsening of disease-related symptoms (n = 9), exam/radiographic changes (n = 7), and laboratory changes (n = 8). An estimated one in every three patients discontinued ibrutinib by 2 years, with 25% developing rapid disease progression afterwards.

Accumulation of JAK activation loop phosphorylation is linked to type I JAK inhibitor withdrawal syndrome in myelofibrosis

Treatment of patients with myelofibrosis with the type I JAK (Janus kinase) inhibitor ruxolitinib paradoxically induces JAK2 activation loop phosphorylation and is associated with a life-threatening cytokine-rebound syndrome if rapidly withdrawn. We developed a time-dependent assay to mimic ruxolitinib withdrawal in primary JAK2^V617F and CALR mutant myelofibrosis patient samples and observed notable activation of spontaneous STAT signaling in JAK2^V617F samples after drug washout. Accumulation of ruxolitinib-induced JAK2 phosphorylation was dose dependent and correlated with rebound signaling and the presence of a JAK2^V617F mutation. Ruxolitinib prevented dephosphorylation of a cryptic site involving Tyr^1007/1008 in JAK2 blocking ubiquitination and degradation. In contrast, a type II JAK inhibitor, CHZ868, did not induce JAK2 phosphorylation, was not associated with withdrawal signaling, and was superior in the eradication of flow-purified JAK2^V617F mutant CD34⁺ progenitors after drug washout. Type I inhibitor-induced loop phosphorylation may act as a pathogenic signaling node released upon drug withdrawal, especially in JAK2^V617F patients.

Acute respiratory distress syndrome; A rare complication caused by usage of ruxolitinib

Ruxolitinib-associated acute respiratory distress has rarely been reported, mostly due to discontinuation of treatment. Herein we report a 58-year-old male patient with primary myelofibrosis who presented with malaise and dyspnea 15 days after initiation of the treatment. The patient was diagnosed as mild acute respiratory distress syndrome (ARDS). After excluding other potential causes such as infection and cardiac pathologies, it was considered secondary to ruxolitinib use. The medication was discontinued and 1 mg/kg methylprednisolone was given to prevent cytokine rebound syndrome and continuous positive airway pressure therapy was prescribed for ARDS. Symptomatic improvement and complete radiological resolution was observed. This case suggests that ARDS may develop secondary to ruxolitinib use and ARDS should be keep in mind in the cases with respiratory symptoms who were on treatment.

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.

Ruxolitinib: evolution or revolution in treatment of patients with polycythemia vera?

Current treatments for polycythemia vera have remained unchanged for decades with phlebotomy, hydroxycarbamide (also named hydroxyurea) and to a lesser extent interferon being the cornerstones in our therapeutic armamentarium. However, some patients do not respond to, or indeed experience significant side effects to, these current agents and development of alternative therapeutic options is required. Ruxolitinib, a potent JAK1/2 inhibitor, initially approved for myelofibrosis, was recently approved for patients with polycythemia vera refractory or intolerant to hydroxycarbamide. In this article, we review the currently available efficacy and safety data.

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.

Definition and management of ruxolitinib treatment failure in myelofibrosis

Ruxolitinib, a Janus kinase (JAK)-1 and JAK-2 inhibitor, is the first-in-class drug to be licensed in the United States for the treatment of high- and intermediate-risk myelofibrosis (MF). Several other JAK inhibitors are in development with some currently undergoing phase-3 clinical trial testing. None of the currently available JAK inhibitors are specific to mutant JAK2; their mechanism of action involves attenuation of JAK-STAT signaling with downregulation of proinflammatory cytokines, rather than selective suppression of the disease clone. Accordingly, while ruxolitinib and other JAK inhibitors are effective in controlling splenomegaly and alleviating constitutional symptoms, their benefit in terms of reversing bone marrow fibrosis or inducing complete or partial remissions appears to be limited. The experience to date with ruxolitinib shows that despite its salutary effects on quality of life, over half of the patients discontinue treatment within 2-3 years. In the current perspective, we examine the incidence and causes of ruxolitinib 'treatment failure' in MF patients based on our personal experience as well as a review of the published literature. We also discuss the challenges in defining and classifying ruxolitinib failure, and within the context of several clinical scenarios, we provide recommendations for the post-ruxolitinib management of MF patients.