Analysis of predictors of response to ruxolitinib in patients with myelofibrosis in the phase 3b expanded-access JUMP study

Methodological challenges in the development of endpoints for myelofibrosis clinical trials

Myelofibrosis is a myeloid neoplasm characterised by the presence of JAK2, CALR, or MPL mutations (with a 90% mutation frequency) and trilineage myeloid proliferation with prominent megakaryocyte atypia. People with myelofibrosis have a lower survival rate and poorer quality of life than healthy individuals. Therapy for myelofibrosis uses Janus kinase inhibitors, which reduce splenomegaly and alleviate symptoms. Regulatory approvals for Janus kinase inhibitors have focused on this dual endpoint. In this Viewpoint, we discuss the validity of using spleen reduction as a surrogate endpoint for the disease-modifying activity of candidate drugs for myelofibrosis. We suggest alternative endpoints addressing unmet patient needs, including progression-free survival and overall survival. Moreover, we highlight the importance of selecting a core set of crucial outcomes with which we can individualise clinical decision making and standardise reporting of clinical trials results. We propose selecting patient-reported outcomes and anaemia response. We also suggest integrating economic considerations in the process of evaluating new drugs for myelofibrosis.

The role of therapy in the outcome of patients with myelofibrosis

BACKGROUND

The treatment of patients with myelofibrosis (MF) has evolved in the past decade, as reflected in an increased use of various therapeutic agents that could potentially impact patient outcomes.

METHODS

In this retrospective study, the authors evaluated the pattern of therapy and its possible impact on the survival of patients with MF at their institution. Patients (n = 802) with newly diagnosed, chronic, overt MF (MF fibrosis grade ≥2, <10% blasts) seen at their cancer center between 2000 and 2020 were included.

RESULTS

Overall, 492 of the included patients (61%) initiated MF-directed therapy during follow-up. The most frequent initial therapy was the JAK inhibitor ruxolitinib (44% of treated patients), investigational agents excluding JAK inhibitors (21%), immunomodulatory agents (18%), other investigational JAK inhibitors (10%), and others (7%). Overall survival was superior for patients who received initial ruxolitinib therapy, with a median survival of 72 months versus approximately 50 months for the remaining approaches, excluding the last group. Thirty-two percent of patients required subsequent therapy (n = 159). The longest survival since the start of second-line therapy was observed in patients who initiated salvage ruxolitinib (median, 35 months; 95% CI, 25-45 months).

CONCLUSIONS

This study demonstrated improved outcomes of patients with MF who received treatment with the JAK inhibitor ruxolitinib.

Relevant Clinical Factors in Patients with Myelofibrosis on Ruxolitinib for 5 or More Years

INTRODUCTION

Median duration of therapy with the first JAK1/2 inhibitor ruxolitinib (RUX) approved for patients with intermediate or high-risk myelofibrosis (MF) is about 3 years.

METHODS

In this retrospective study, we aimed to evaluate clinical features, predictive factors, and outcome of patients presenting to our institution who were able to remain on RUX for ≥5 years (RUX ≥5y, n = 73).

RESULTS

Comparing baseline demographics of patients who remained on RUX ≥5y (n = 73) with patients who were on RUX for 6 months to 3 years (n = 203), we confirmed that patients on RUX ≥5y lacked advanced clinical features at the start of therapy, such as anemia, neutropenia, thrombocytopenia, higher blasts or monocytes. Predictive independent factors for staying on RUX ≥5y were hemoglobin >10 g/dL, circulating blasts <1%, platelets >150 × 109/L, neutrophils >70%, and having primary MF. Age over 65 years remained significant for outcome in patients on RUX ≥5y.

CONCLUSION

In this retrospective study, we report on the relevance of absence of advanced clinical features for long RUX therapy and confirm the role of age on outcome despite therapy.

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.

Benefit of Early Ruxolitinib Initiation Regardless of Fibrosis Grade in Patients with Primary Myelofibrosis: A Post Hoc Analysis of the Single-Arm Phase 3b JUMP Study

Bone marrow fibrosis (BMF) is an adverse prognostic factor for myelofibrosis (MF). The single-arm, open-label, phase 3b JUMP trial (NCT01493414) assessed the safety and efficacy of the JAK1/JAK2 inhibitor ruxolitinib in patients with symptomatic MF. This post hoc analysis investigated the impact of BMF grade on response and outcomes in patients with primary MF (PMF) from the JUMP study. BMF was assessed by biopsy and graded from 0 to 3; grades 0-1 were considered low-grade fibrosis (LGF) and grades 2-3 were considered high-grade fibrosis (HGF). Patients with LGF (n = 268) had lower rates of cytopenias at baseline but showed comparable disease burden vs. patients with HGF (n = 852). The proportion of patients achieving a spleen response was greater in the LGF group vs. the HGF group at Week 24 and at any time during the study, while overall survival estimates were improved in patients with LGF vs. patients with HGF. Early initiation of ruxolitinib therapy (within 2 years of diagnosis) was associated with increased response rates in all patients. These results highlight the efficacy of ruxolitinib in symptomatic patients with PMF, with the greatest clinical improvements observed in patients with LGF and in patients who received early treatment.

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.

How I manage anemia related to myelofibrosis and its treatment regimens

Myelofibrosis (MF) is a myeloproliferative neoplasm characterized by mutations (most frequently in JAK2, CALR, or MPL), burdensome symptoms, splenomegaly, cytopenia, and shortened life expectancy. In addition to other clinical manifestations, patients with MF often develop anemia, which can either be directly related to MF pathogenesis or a result of MF treatment with Janus kinase (JAK) inhibitors, such as ruxolitinib and fedratinib. Although symptoms and clinical manifestations can be similar between the 2 anemia types, only MF-related anemia is prognostic of reduced survival. In this review, I detail treatment and patient management approaches for both types of anemia presentations and provide recommendations for the treatment of MF in the presence of anemia.

Early intervention in myelofibrosis and impact on outcomes: A pooled analysis of the COMFORT-I and COMFORT-II studies

BACKGROUND

In a pooled analysis of the phase 3 Controlled Myelofibrosis Study With Oral JAK Inhibitor Treatment I (COMFORT-I) and COMFORT-II clinical trials, adult patients with intermediate-2 or high-risk myelofibrosis who received oral ruxolitinib at randomization or after crossover from placebo or best available therapy (BAT) had improved overall survival (OS).

METHODS

This post hoc analysis of pooled COMFORT data examined relevant disease outcomes based on the disease duration (≤12 or >12 months from diagnosis) before ruxolitinib initiation.

RESULTS

The analysis included 525 patients (ruxolitinib: ≤12 months, n = 84; >12 months, n = 216; placebo/BAT: ≤12 months, n = 66; >12 months, n = 159); the median age was 65.0-70.0 years. Fewer thrombocytopenia and anemia events were observed among patients who initiated ruxolitinib treatment earlier. At Weeks 24 and 48, the spleen volume response (SVR) was higher for patients who initiated ruxolitinib earlier (47.6% vs. 32.9% at Week 24, p = .0610; 44.0% vs. 26.9% at Week 48, p = .0149). In a multivariable analysis of factors associated with spleen volume reduction, a logistic regression model that controlled for confounding factors found that a significantly greater binary reduction was observed among patients with shorter versus longer disease duration (p = .022). At Week 240, OS was significantly improved among patients who initiated ruxolitinib earlier (63% [95% CI, 51%-73%] vs. 57% [95% CI, 49%-64%]; hazard ratio, 1.53; 95% CI, 1.01-2.31; p = .0430). Regardless of disease duration, a longer OS was observed for patients who received ruxolitinib versus those who received placebo/BAT.

CONCLUSIONS

These findings suggest that earlier ruxolitinib initiation for adult patients with intermediate-2 and high-risk myelofibrosis may improve clinical outcomes, including fewer cytopenia events, durable SVR, and prolonged OS.

PLAIN LANGUAGE SUMMARY

Patients with myelofibrosis, a bone marrow cancer, often do not live as long as the general population. These patients may also have an enlarged spleen and difficult symptoms such as fatigue. Two large clinical trials showed that patients treated with the drug ruxolitinib lived longer and had improved symptoms compared to those treated with placebo or other standard treatments. Here it was examined whether starting treatment with ruxolitinib earlier (i.e., within a year of diagnosis) provided benefits versus delaying treatment. Patients who received ruxolitinib within a year of diagnosis lived longer and experienced fewer disease symptoms than those whose treatment was delayed.

Analysis of Predictive Factors for Early Response to Ruxolitinib in 320 Patients with Myelofibrosis From the Polish Adult Leukemia Group (PALG) Registry

INTRODUCTION

Ruxolitinib is widely used in myelofibrosis (MF). However, some patients do not optimally respond and require more efficacious treatment. Our analysis aimed to establish predictors of ruxolitinib response.

PATIENTS AND METHODS

We designed a multicenter, retrospective analysis of the efficacy of ruxolitinib treatment in patients with MF in 15 Polish hematology centers. As responses to ruxolitinib occur within the first 6 months, we used this point to evaluate the efficacy of treatment. Symptoms response was defined as ≥50% reduction of the MF constitutional symptoms assessed by Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score (MPN-SAF TSS). Spleen response was defined as ≥50% reduction of the difference between the spleen's baseline length and the upper limit norm measured by ultrasonography.

RESULTS

320 MF patients were enrolled. At 6 months of therapy, the spleen response was detected in 140 (50%) patients, and symptoms response in 241 patients (76%). Multivariable analysis identified leukocytosis <25 G/L (OR 2.06, 95%CI: 1.12-3.88, P = .0200), and reticulin fibrosis MF 1 (OR 2.22, 95%CI: 1.11-4.46, P = .0249) contributed to better spleen response. The time interval between MF diagnosis and ruxolitinib administration shorter than 3 months, and platelets ≥150 G/L (OR 1.69, 95% CI 1.01-2.83, P = .0466) influenced symptoms response.

CONCLUSION

Establishing predictive factors for ruxolitinib response is particularly important given the potential for new therapies in MF. In patients with a low likelihood of responding to ruxolitinib, using other JAK inhibitors or adding a drug with a different mechanism of action to ruxolitinib may be of clinical benefit.

Fedratinib: a pharmacotherapeutic option for JAK-inhibitor naïve and exposed patients with myelofibrosis

INTRODUCTION

Ruxolitinib is the most commonly used JAK-inhibitor (JAKi) for the management of symptoms related to splenomegaly and cytokine-mediated inflammation in patients with myelofibrosis (MF), but is limited by variable durability of response with most patients experiencing failure after 2-3 years. Long-term data on other approved JAKi, fedratinib and pacritinib, are not available due to the clinical hold put on pivotal trials for toxicity concerns.

AREAS COVERED

Following the initial hold for concern of Wernicke's encephalopathy, fedratinib was approved by the Food and Drug Administration (FDA) in 2019 for MF. We review the data available from early, and late phase critical trials, outline a role for fedratinib in the current treatment landscape of MF, and highlight the knowledge gaps in optimizing use of fedratinib.

EXPERT OPINION

The JAKARTA and JAKARTA2 trials established efficacy in spleen volume response (SVR) and symptom reduction in JAKi-naïve and ruxolitinib-exposed MF patients, respectively. Further trials, FREEDOM and FREEDOM2, are in progress to understand long-term effects of fedratinib; and include strategies to mitigate gastrointestinal toxicity, monitor thiamine levels and surveil for encephalopathy. We use fedratinib for symptomatic MF following ruxolitinib failure in patients without significant cytopenias; with practical strategies for monitoring and managing potential toxicity.

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.

Real-world clinical outcomes of patients with myelofibrosis treated with ruxolitinib: a medical record review

Aim: To assess real-world ruxolitinib treatment patterns and outcomes in patients diagnosed with primary or secondary myelofibrosis. Materials & methods: Patient medical records were reviewed in six countries. Results: Eligible patients (n = 469) had a mean age of 63.5 years, and most were male (66.5%) with primary myelofibrosis (78.5%). Median duration of ruxolitinib treatment was 13.1 months; 40% of patients initiated treatment at the recommended dose. The Kaplan-Meier estimate of median survival from ruxolitinib initiation was 44.4 months (95% CI, 38.8-50.2 months). Approximately one quarter (23%) of patients continued ruxolitinib after progression. Conclusion: These results suggest an unmet need for more effective treatments for patients with myelofibrosis who failed ruxolitinib.

The clinical dilemma of JAK inhibitor failure in myelofibrosis: Predictive characteristics and outcomes

Two Janus‐associated kinase inhibitors (JAKi) (initially ruxolitinib and, more recently, fedratinib) have been approved as treatment options for patients who have intermediate‐risk and high‐risk myelofibrosis (MF), with pivotal trials demonstrating improvements in spleen volume, disease symptoms, and quality of life. At the same time, however, clinical trial experiences with JAKi agents in MF have demonstrated a high frequency of discontinuations because of adverse events or progressive disease. In addition, overall survival benefits and clinical and molecular predictors of response have not been established in this population, for which the disease burden is high and treatment options are limited. Consistently poor outcomes have been documented after JAKi discontinuation, with survival durations after ruxolitinib ranging from 11 to 16 months across several studies. To address such a high unmet therapeutic need, various non‐JAKi agents are being actively explored (in combination with ruxolitinib in first‐line or salvage settings and/or as monotherapy in JAKi‐pretreated patients) in phase 3 clinical trials, including pelabresib (a bromodomain and extraterminal domain inhibitor), navitoclax (a B‐cell lymphoma 2/B‐cell lymphoma 2‐xL inhibitor), parsaclisib (a phosphoinositide 3‐kinase inhibitor), navtemadlin (formerly KRT‐232; a murine double‐minute chromosome 2 inhibitor), and imetelstat (a telomerase inhibitor). The breadth of data expected from these trials will provide insight into the ability of non‐JAKi treatments to modify the natural history of MF.

Janus‐associated kinase inhibitor (JAKi) agents improved spleen volume and symptoms in patients who had myelofibrosis but were associated with high discontinuation rates, a lack of predictors of response, and poor outcomes after discontinuation. Non‐JAKi agents, in combination with or subsequent to JAK agents, were being actively explored in phase 3 clinical trials.

A Prognostic Model to Predict Survival After 6 Months of Ruxolitinib in Patients with Myelofibrosis

RUX dose, spleen response, and transfusion requirement in the first 6 months of RUX treatment predict overall survival in MF.

The RR6 model overcomes conventional risk stratification in RUX-treated MF.

Ruxolitinib (RUX) is extensively used in myelofibrosis (MF). Despite its early efficacy, most patients lose response over time and, after discontinuation, have a worse overall survival (OS). Currently, response criteria able to predict OS in RUX-treated patients are lacking, leading to uncertainty regarding the switch to second-line treatments. In this study, we investigated predictors of survival collected after 6 months of RUX in 209 MF patients participating in the real-world ambispective observational RUXOREL-MF study (NCT03959371). Multivariable analysis identified the following risk factors: (1) RUX dose <20 mg twice daily at baseline, months 3 and 6 (hazard ratio [HR], 1.79; 95% confidence interval [CI], 1.07-3.00; P = .03), (2) palpable spleen length reduction from baseline ≤30% at months 3 and 6 (HR, 2.26; 95% CI, 1.40-3.65; P = .0009), (3) red blood cell (RBC) transfusion need at months 3 and/or 6 (HR, 1.66; 95% CI, 0.95-2.88; P = .07), and (4) RBC transfusion need at all time points (ie, baseline and months 3 and 6; HR, 2.32; 95% CI, 1.19-4.54; P = .02). Hence, we developed a prognostic model, named Response to Ruxolitinib After 6 Months (RR6), dissecting 3 risk categories: low (median OS, not reached), intermediate (median OS, 61 months; 95% CI, 43-80), and high (median OS, 33 months; 95% CI, 21-50). The RR6 model was validated and confirmed in an external cohort comprised of 40 MF patients. In conclusion, the RR6 prognostic model allows for the early identification of RUX-treated MF patients with impaired survival who might benefit from a prompt treatment shift.

Updated recommendations on the use of ruxolitinib for the treatment of myelofibrosis

OBJECTIVES

Myelofibrosis is a rare bone marrow disorder associated with a high symptom burden, poor prognosis, and shortened survival. While allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative treatment for myelofibrosis, the only approved and reimbursed pharmacotherapy for non-HSCT candidates in Belgium is ruxolitinib.

METHODS

These updated recommendations are based on a consensus reached during two meetings and provide guidance for ruxolitinib administration in myelofibrosis patients considering the particularities of Belgian reimbursement criteria.

RESULTS AND DISCUSSION

In Belgium, ruxolitinib is indicated and reimbursed for transplant-ineligible myelofibrosis patients from intermediate-2- and high-risk groups and from the intermediate-1-risk group with splenomegaly. Our recommendation is to also make ruxolitinib available in the pre-transplant setting for myelofibrosis patients with splenomegaly or heavy symptom burden. Before ruxolitinib initiation, complete blood cell counts are recommended, and the decision on the optimal dosage should be based on platelet count and clinical parameters. In anemic patients, we recommend starting doses of ruxolitinib of 10 mg twice daily for 12 weeks and we propose the use of erythropoiesis-stimulating agents in patients with endogenous erythropoietin levels ≤500 mU/mL. Increased vigilance for opportunistic infections and second primary malignancies is needed in ruxolitinib-treated myelofibrosis patients. Ruxolitinib treatment should be continued as long as there is clinical benefit (reduced splenomegaly or symptoms), and we recommend progressive dose tapering when stopping ruxolitinib.

CONCLUSION

Based on new data and clinical experience, the panel of experts discussed ruxolitinib treatment in Belgian myelofibrosis patients with a focus on dose optimization/monitoring, adverse events, and interruption/rechallenge management.

Novel therapies vs hematopoietic cell transplantation in myelofibrosis: who, when, how?

Myelofibrosis is one of the classical Philadelphia chromosome-negative myeloproliferative neoplasms characterized by progressive marrow failure and chronic inflammation. Discovery of the JAK2 mutation paved the way for development of small molecular inhibitors and further facilitated the research in understanding of molecular biology of the disease. Development of novel medications and synergistic combinations with standard JAK inhibitor (JAKi) therapy may have the potential to improve depth and duration of disease control and symptomatic benefit, whereas advancements in allogeneic hematopoietic stem cell transplantation (HCT) have improved tolerability and donor availability, allowing for more patients to pursue this potentially curative therapy. The increase in options for medical therapy and changing risk profile of HCT is leading to increased complexity in counseling patients on choice of management strategy. In this case-based review, we summarize our approach to symptom-directed medical therapy, including the use of novel drugs and combination therapies currently under study in advanced clinical trials. We outline our recommendations for optimal timing of HCT, including risk-adapted selection for early HCT as opposed to delayed HCT after upfront JAKi therapy, as well as the use of pretransplant JAKi and alternative donor sources.

Emerging drugs for the treatment of myelofibrosis: phase II & III clinical trials

INTRODUCTION

Myelofibrosis is a clonal hematologic malignancy with clinical manifestations that include cytopenias, debilitating constitutional symptoms, splenomegaly, bone marrow fibrosis and a propensity toward leukemic progression. While allogeneic hematopoietic stem cell transplantation can be curative, this therapy is not available for the majority of patients. Ruxolitinib and fedratinib are approved JAK2 inhibitors that have produced meaningful benefits in terms of spleen reduction and symptom improvement, but there remain several unmet needs.

AREAS COVERED

We discuss novel therapies based upon published data from phase II or III clinical trials. Specifically, we cover novel JAK inhibitors (momelotinib and pacritinib), and agents that target bromodomain and extra-terminal domain (pelabresib), the antiapoptotic proteins BCL-2/BCL-xL (navitoclax), MDM2 (navtemadlin), phosphatidylinositol 3-kinase (parsaclisib), or telomerase (imetelstat).

EXPERT OPINION

Patients with disease related cytopenias are ineligible for currently approved JAK2 inhibitors. However, momelotinib and pacritinib may be able to fill this void. Novel therapies are being evaluated in the upfront setting to improve the depth and duration of responses with ruxolitinib. Future evaluation of agents must be judged on their potential to modify disease progression, which current JAK2 inhibitors lack. Combination therapy, possibly with an immunotherapeutic agent might serve as key components of future myelofibrosis treatment options.

Efficacy and safety of a novel dosing strategy for ruxolitinib in the treatment of patients with myelofibrosis and anemia: the REALISE phase 2 study

Anemia is a frequent manifestation of myelofibrosis (MF) and there is an unmet need for effective treatments in anemic MF patients. The REALISE phase 2 study (NCT02966353) evaluated the efficacy and safety of a novel ruxolitinib dosing strategy with a reduced starting dose with delayed up-titration in anemic MF patients. Fifty-one patients with primary MF (66.7%), post-essential thrombocythemia MF (21.6%), or post-polycythemia vera MF (11.8%) with palpable splenomegaly and hemoglobin <10 g/dl were included. Median age was 67 (45–88) years, 41.2% were female, and 18% were transfusion-dependent. Patients received 10 mg ruxolitinib b.i.d. for the first 12 weeks, then up-titrations of up to 25 mg b.i.d. were permitted, based on efficacy and platelet counts. Overall, 70% of patients achieved a ≥50% reduction in palpable spleen length at any time during the study. The most frequent adverse events leading to dose interruption/adjustment were thrombocytopenia (17.6%) and anemia (11.8%). Patients who had a dose increase had greater spleen size and higher white blood cell counts at baseline. Median hemoglobin levels remained stable and transfusion requirements did not increase compared with baseline. These results reinforce the notion that it is unnecessary to delay or withhold ruxolitinib because of co-existent or treatment-emergent anemia.