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

Top advances of the year: Myeloproliferative neoplasms

The rapid pace of drug development in hematology has led to multiple approvals for myelofibrosis (MF) and polycythemia vera (PV) in recent years. Moreover, there are many innovative agents and combinations being explored for myeloproliferative neoplasms (MPNs). In the past year, there have been several advances in MF, PV, and essential thrombocythemia. In MF, investigational approaches are focusing on strategies to optimize inhibition of signal transduction (including JAK inhibition), modify epigenetics, enhance apoptosis, target DNA replication, transform host immunity, and/or alter the tumor microenvironment. In PV, ropeginterferon alfa-2b has been introduced to the market in the United States, and data continue to accumulate to support the safety and efficacy of this treatment. Hepcidin mimesis is also emerging as a novel way to treat erythrocytosis. In essential thrombocythemia, ropeginterferon alfa-2b is being evaluated, as are therapies to modify epigenetics and inhibit CALR. The enhanced focus on MPNs brings hope that our field can improve morbidity and mortality in this group of diseases.

Momelotinib in Myelofibrosis Patients With Thrombocytopenia: Post Hoc Analysis From Three Randomized Phase 3 Trials

The oral activin A receptor type I, Janus kinase 1 (JAK1), and JAK2 inhibitor momelotinib demonstrated symptom, spleen, and anemia benefits in intermediate- and high-risk myelofibrosis (MF). Post hoc analyses herein evaluated the efficacy and safety of momelotinib in patients with MF and thrombocytopenia (platelet counts <100 × 109/L) from randomized phase 3 studies: MOMENTUM (momelotinib versus danazol; JAK inhibitor experienced); SIMPLIFY-1 (momelotinib versus ruxolitinib; JAK inhibitor naïve); and SIMPLIFY-2 (momelotinib versus best available therapy; JAK inhibitor experienced); these studies were not statistically powered to assess differences in thrombocytopenic subgroups, and these analyses are descriptive. The treatment effect of momelotinib versus ruxolitinib on week 24 response rates (spleen volume reduction ≥35%/Total Symptom Score reduction ≥50%/transfusion independence) was numerically comparable or better in thrombocytopenic patients versus the overall JAK inhibitor naive population; rates were preserved with momelotinib in thrombocytopenic patients but attenuated with ruxolitinib (momelotinib: 27%/28%/67% overall versus 39%/35%/61% in thrombocytopenic group; ruxolitinib: 29%/42%/49% overall versus 0%/22%/39% in thrombocytopenic group, respectively). In contrast to ruxolitinib, momelotinib maintained high dose intensity throughout the treatment. In the JAK inhibitor experienced population, thrombocytopenic patients had the following: (1) numerically higher symptom and transfusion independence response rates with momelotinib than in control arms; and (2) preserved spleen, symptom, and transfusion independence response rates with momelotinib relative to the overall study populations. The safety profile of momelotinib in thrombocytopenic patients was also consistent with the overall study population. In summary, momelotinib represents a safe and effective treatment option for patients with MF and moderate-to-severe thrombocytopenia.

Pacritinib is a potent ACVR1 inhibitor with significant anemia benefit in patients with myelofibrosis

In patients with cytopenic myelofibrosis, treatment with the JAK2/IRAK1 inhibitor pacritinib was associated with anemia benefit in the phase 3 PERSIST-2 study. The impact of pacritinib on transfusion independence (TI) has not been previously described, nor has the mechanism by which pacritinib improves anemia been elucidated. Because it has been previously postulated that inhibition of activin A receptor, type 1 (ACVR1)/activin receptor-like kinase-2 improves anemia in patients with myelofibrosis via suppression of hepcidin production, we assessed the relative inhibitory potency of pacritinib compared with other JAK2 inhibitors against ACVR1. Pacritinib inhibited ACVR1 with greater potency (half-maximal inhibitory concentration [IC50] = 16.7 nM; Cmax:IC50 = 12.7) than momelotinib (IC50 = 52.5 nM; Cmax:IC50 = 3.2), fedratinib (IC50 = 273 nM; Cmax:IC50 = 1.0), or ruxolitinib (IC50 > 1000; Cmax:IC50 < 0.01). Pacritinib's inhibitory activity against ACVR1 was corroborated via inhibition of downstream SMAD signaling in conjunction with marked suppression of hepcidin production. Among patients on PERSIST-2 who were not transfusion independent at baseline based on Gale criteria, a significantly greater proportion achieved TI on pacritinib compared with those treated on best available therapy (37% vs 7%, P = .001), and significantly more had a ≥50% reduction in transfusion burden (49% vs 9%, P < .0001). These data indicate that the anemia benefit of the JAK2/IRAK1 inhibitor pacritinib may be a function of potent ACVR1 inhibition.

Safety and efficacy of zinpentraxin alfa as monotherapy or in combination with ruxolitinib in myelofibrosis: stage I of a phase II trial

Pentraxin 2 (PTX-2; serum amyloid P component), a circulating endogenous regulator of the inflammatory response to tissue injury and fibrosis, is reduced in patients with myelofibrosis (MF). Zinpentraxin alfa (RO7490677, PRM-151) is a recombinant form of PTX-2 that has shown preclinical antifibrotic activity and no dose-limiting toxicities in phase I trials. We report results from stage 1 of a phase II trial of zinpentraxin alfa in patients with intermediate-1/2 or high-risk MF. Patients (n=27) received intravenous zinpentraxin α weekly (QW) or every 4 weeks (Q4W), as monotherapy or an additional therapy for patients on stable-dose ruxolitinib. The primary endpoint was overall response rate (ORR; investigatorassessed) adapted from International Working Group-Myeloproliferative Neoplasms Research and Treatment criteria. Secondary endpoints included modified Myeloproliferative Neoplasm-Symptom Assessment Form Total Symptom Score (MPN-SAF TSS) change, bone marrow (BM) MF grade reduction, pharmacokinetics, and safety. ORR at week 24 was 33% (n=9/27) and varied across individual cohorts (QW: 38% [3/8]; Q4W: 14% [1/7]; QW+ruxolitinib: 33% [2/6]; Q4W+ruxolitinib: 50% [3/6]). Five of 18 evaluable patients (28%) experienced a ≥50% reduction in MPN-SAF TSS, and six of 17 evaluable patients (35%) had a ≥1 grade improvement from baseline in BM fibrosis at week 24. Most treatment-emergent adverse events (AE) were grade 1-2, most commonly fatigue. Among others, anemia and thrombocytopenia were infrequent (n=3 and n=1, respectively). Treatment-related serious AE occurred in four patients (15%). Overall, zinpentraxin alfa showed evidence of clinical activity and tolerable safety as monotherapy and in combination with ruxolitinib in this open-label, non-randomized trial (clinicaltrials gov. Identifier: NCT01981850).

High molecular risk variants, severe thrombocytopenia and large unstained cells count affect the outcome in primary myelofibrosis

Apart from the driver mutations, high molecular risk (HMR) variants and other factors have been reported to influence the prognosis of primary myelofibrosis (PMF). The aim of our study was to investigate the impact of laboratory and molecular characteristics at the time of diagnosis (TOD) on the PMF outcome. The study group consisted of 82 patients recruited from three Polish university centers. Among the driver mutations, only CALR type 1 positively influenced the overall survival (OS). The risk of progression to accelerated or blastic disease phase (AP/BP) did not depend on the driver mutation type, but was closely associated with the presence of HMR variants (p = 0.0062). The risk of death (ROD) was higher in patients with HMR variants (OR[95%CI] = 4.33[1.52;12.34], p = 0.0044) and in patients with a platelet count at the TOD between 50-100 G/L (HR[95%CI] = 2.66[1.11;6.35]) and < 50 G/L (HR[95%CI] = 8.44[2.50;28.44]). Median survival time was 7.8, 2.2 and 1.4 years in patients with large unstained cells (LUC) count of [0.0-0.2], (0.2-0.4] and > 0.4 G/L at the TOD, respectively. We found an unexpected, hitherto undescribed, association between LUC count at the TOD and PMF prognosis. Our analysis led to the following conclusions: in PMF patients at the TOD 1) the presence of HMR variants, especially combined, is associated with an increased risk of progression to the AP and BP, and shorter OS, 2) severe thrombocytopenia confers worse prognosis than the moderate one, 3) LUC count is closely related with the disease phase, and associated with the ROD and OS.

Association of Myelofibrosis Phenotypes with Clinical Manifestations, Molecular Profiles, and Treatments

Myelofibrosis (MF) presents an array of clinical manifestations and molecular profiles. The two distinct phenotypes- myeloproliferative and myelodepletive or cytopenic- are situated at the two poles of the disease spectrum and are largely defined by different degrees of cytopenias, splenomegaly, and distinct molecular profiles. The myeloproliferative phenotype is characterized by normal/higher peripheral blood counts or mildly decreased hemoglobin, progressive splenomegaly, and constitutional symptoms. The myeloproliferative phenotype is typically associated with secondary MF, higher JAK2 V617F burden, fewer mutations, and superior overall survival (OS). The myelodepletive phenotype is usually associated with primary MF, ≥2 cytopenias, modest splenomegaly, lower JAK2 V617F burden, higher fibrosis, greater genomic complexity, and inferior OS. Cytopenias are associated with mutations in epigenetic regulators/splicing factors, clonal evolution, disease progression, and shorter OS. Clinical variables, in conjunction with the molecular profiles, inform integrated prognostication and disease management. Ruxolitinib/fedratinib and pacritinib/momelotinib may be more suitable to treat patients with the myeloproliferative and myelodepletive phenotypes, respectively. Appreciation of MF heterogeneity and two distinct phenotypes, the different clinical manifestations and molecular profiles associated with each phenotype alongside the growing treatment expertise, the development of non-myelosuppressive JAK inhibitors, and integrated prognostication are leading to a new era in patient management. Physicians can increasingly tailor personalized treatments that will address the unique unmet needs of MF patients, including those presenting with the myelodepletive phenotype, to elicit optimal outcomes and extended OS across the disease spectrum.

SOHO State of the Art Updates and Next Questions: Novel Therapeutic Strategies in Development for Myelofibrosis

Development of myelofibrosis (MF) therapeutics has reached fruition as the transformative impact of JAK2 inhibitors in the MPN landscape is complemented/expanded by a profusion of novel monotherapies and rational combinations in the frontline and second line settings. Agents in advanced clinical development span various mechanisms of action (eg, epigenetic or apoptotic regulation), may address urgent unmet clinical needs (cytopenias), increase the depth/duration of spleen and symptom responses elicited by ruxolitinib, improve other aspects of the disease besides splenomegaly/constitutional symptoms (eg, resistance to ruxolitinib, bone marrow fibrosis or disease course), provide personalized strategies, and extend overall survival (OS). Ruxolitinib had a dramatic impact on the quality of life and OS of MF patients. Recently, pacritinib received regulatory approval for severely thrombocytopenic MF patients. Momelotinib is advantageously poised among JAK inhibitors given its differentiated mode of action (suppression of hepcidin expression). Momelotinib demonstrated significant improvements in anemia measures, spleen responses, and MF-associated symptoms in MF patients with anemia; and will likely receive regulatory approval in 2023. An array of other novel agents combined with ruxolitinib, such as pelabresib, navitoclax, parsaclisib, or as monotherapies (navtemadlin) are evaluated in pivotal phase 3 trials. Imetelstat (telomerase inhibitor) is currently evaluated in the second line setting; OS was set as the primary endpoint, marking an unprecedented goal in MF trials, wherein SVR35 and TSS50 at 24 weeks have been typical endpoints heretofore. Transfusion independence may be considered another clinically meaningful endpoint in MF trials given its correlation with OS. Overall, therapeutics are at the cusp of an exponential expansion and advancements that will likely lead to the golden era in treatment of MF.

Comparison of Pretransplantation Prediction Models for Nonrelapse Mortality in Patients with Myelofibrosis Undergoing Allogeneic Stem Cell Transplantation

Allogeneic stem cell transplantation (alloSCT) is the only known curative treatment for myelofibrosis (MF). Risk assessment remains important for patient counseling and predicting survival outcomes for relapse and nonrelapse mortality (NRM). Outcome-prediction tools can guide decision-making. Their use in MF has relied on their extrapolation from other malignancies. The primary objective of this study was to assess the performance of the Hematopoietic cell Transplantation Comorbidity Index (HCT-CI), the augmented HCT-CI (aHCT-CI), and the Endothelial Activation and Stress Index (EASIX) in predicting NRM in patients with MF undergoing alloSCT. We retrospectively reviewed patients with MF undergoing alloSCT between 2012 and 2020 at the Mayo Clinic. Data were abstracted from the electronic medical record. EASIX score was calculated before starting conditioning therapy and analyzed based on log2- transformed values. We evaluated the log2-EASIX scores by quartiles to assess the effect of increasing values on NRM. NRM was evaluated using competing risk analyses. We used the Kaplan-Meier and log-rank methods to evaluate OS. The Fine-Gray model was used to determine risk factors for NRM. The performance of HCT-CI and aHCT-CI was compared by evaluation of model concordance given the high correlation between HCT-CI and aHCT-CI (r = .75). A total of 87 patients were evaluated. The median duration of follow-up after alloSCT was 5 years (95% confidence interval [CI], 4.4 to 6.31 years). Patients with a high HCT-CI score had significantly increased cumulative incidence of NRM at 3 years (35.5% versus 11.6%; P = .011) after alloSCT. A progressively increasing 3-year NRM was observed with increasing aHCT-CI risk category, and patients with a high or very high aHCT-CI score had significantly higher 3-year NRM compared to those with intermediate-risk or low-risk aHCT-CI scores at 3 years post-alloSCT (31.9% versus 6.52%; P = .004). An increasing log2-EASIX score quartile was not associated with 3-year NRM (19.0% versus 10.1% versus 25% versus 14.3%; P = .59), and the EASIX score was not found to be a predictor of post-transplantation NRM. A high HCT-CI was associated with significantly worse 3-year overall survival (OS) (hazard ratio [HR], 4.41; 95% CI, 1.97 to 9.87; P < .001). A high or very high aHCT-CI was significantly associated with poor 3-year OS (HR, 3.99; 95% CI, 1.56 to 10.22; P = .004). An increasing log2-EASIX score quartile group was not associated with 3-year OS (3-year OS rate, 66.7% versus 80.4% versus 64.6% versus 76.2%; P = .57). The EASIX score should not be used routinely in patients with MF. Both the HCT-CI and the aHCT-CI are accurate in predicting long-term survival outcomes in this patient population. Further studies are important to validate our findings of the role of EASIX in predicting NRM in patients with MF or other myeloproliferative neoplasms undergoing alloSCT. © 2023 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

New approaches to tackle cytopenic myelofibrosis

Myelofibrosis (MF) is a clonal hematopoietic stem cell neoplasm characterized by constitutional symptoms, splenomegaly, and risks of marrow failure or leukemic transformation and is universally driven by Jak/STAT pathway activation. Despite sharing this pathogenic feature, MF disease behavior can vary widely. MF can generally be categorized into 2 distinct subgroups based on clinical phenotype: proliferative MF and cytopenic (myelodepletive) MF. Compared to proliferative phenotypes, cytopenic MF is characterized by lower blood counts (specifically anemia and thrombocytopenia), more frequent additional somatic mutations outside the Jak/STAT pathway, and a worse prognosis. Cytopenic MF presents unique therapeutic challenges. The first approved Jak inhibitors, ruxolitinib and fedratinib, can both improve constitutional symptoms and splenomegaly but carry on-target risks of worsening anemia and thrombocytopenia, limiting their use in patients with cytopenic MF. Supportive care measures that aim to improve anemia or thrombocytopenia are often ineffective. Fortunately, new treatment strategies for cytopenic MF are on the horizon. Pacritinib, selective Jak2 inhibitor, was approved in 2022 to treat patients with symptomatic MF and a platelet count lower than 50 × 109/L. Several other Jak inhibitors are in development to extend therapeutic benefits to those with either anemia or thrombocytopenia. While many other novel non-Jak inhibitor therapies are in development for MF, most carry a risk of hematologic toxicities and often exclude patients with baseline thrombocytopenia. As a result, significant unmet needs remain for cytopenic MF. Here, we discuss clinical implications of the cytopenic MF phenotype and present existing and future strategies to tackle this challenging disease.

Thrombocytopenia in Patients With Myelofibrosis: A Practical Management Guide

Patients with myelofibrosis (MF) frequently develop thrombocytopenia as a consequence of bone marrow fibrosis, splenic sequestration, and myelosuppression from an inflammatory microenvironmental milieu. Thrombocytopenia occurs frequently at diagnosis, worsens with disease progression, is an independent adverse prognostic factor, and limits effective dosing of JAK2 inhibitors. Recently, pacritinib was approved for patients with MF and extreme thrombocytopenia. However, this JAK2/IRAK1 inhibitor is not primarily used to attain improvement in platelet count. In this narrative review, we discuss strategies to specifically address thrombocytopenia in MF patients including immunomodulatory drugs, synthetic androgens, hypomethylating agents and splenectomy, all of which have only modest efficacy in alleviating thrombocytopenia. We also detail transfusion approaches, including diagnostic and therapeutic consideration for platelet transfusion refractoriness. We end by discussing novel therapies, including TGFβ traps and recombinant pentraxin-2, which may increase platelet counts in MF patients. Despite recent therapeutic advancements in MF, there remains a near paucity of agents that can effectively alleviate thrombocytopenia.

Novel Therapies in Myelofibrosis: Beyond JAK Inhibitors

PURPOSE OF REVIEW

To discuss the current treatment paradigm, review novel targets, and summarize completed and ongoing clinical trials that may lead to a paradigm shifts in the management of myelofibrosis (MF).

RECENT FINDINGS

In addition to the recent approval and ongoing late-stage development of multiple novel JAK inhibitors, recent clinical studies demonstrate therapeutic potential of targeting multiple alternate proteins and pathways including BET, MDM2, telomerase, BCL2, LSD1, PI3K, SMAC, and PTX2 in patients with MF. MF is a myeloproliferative neoplasm characterized by clonal proliferation of myeloid cells and bone marrow fibrosis often causing cytopenias, extramedullary hematopoiesis resulting in hepatosplenomegaly, and increased pro-inflammatory cytokine production driving systemic symptoms. A significant proportion of morbidity and mortality is related to the propensity to transform to acute leukemia. Allogeneic hematopoietic stem cell transplantation is the only curative therapy; however, due to the high associated mortality, this treatment is not an option for the majority of patients with MF. Currently, there are three targeted Food and Drug Administration (FDA)-approved therapies for MF which include ruxolitinib, fedratinib, and pacritinib, all part of the JAK inhibitor class. Many patients are unable to tolerate, do not respond, or develop resistance to existing therapies, leaving a large unmet medical need. In this review, we discuss the current treatment paradigm and novel therapies in development for the treatment of MF. We review the scientific rationale of each targeted pathway. We summarize updated clinical data and ongoing trials that may lead to FDA approval of these agents.

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.

Disease-related thrombocytopenia in myelofibrosis is defined by distinct genetic etiologies and is associated with unique prognostic correlates

BACKGROUND

Thrombocytopenia in patients with myelofibrosis (MF) is prognostically detrimental and poses a therapeutic challenge. MF patients with thrombocytopenia are considered high-risk by most prognostic models and their distinct phenotype has given rise to the emerging concept of cytopenic MF. Yet, the mechanisms underlying thrombocytopenia in MF are poorly understood.

METHODS

This study aimed to highlight the genetic mechanisms driving low platelet counts in treatment-naive MF patients, establish their phenotypic correlates, and assess prognostic factors specific to this group of patients.

RESULTS

The authors found that most patients presenting with low platelets had a clear thrombocytopenia-specific genetic abnormality involving a U2AF1 Q157 mutation, deletion 20q, molecular complexity (three or more mutations), or high-risk karyotype. Etiologic clustering did not correlate with prognosis; however, thrombocytopenic patients were found to have unique prognostic variables including low serum albumin and mutations of SRSF2 and TP53. This led to the proposal of a prognostic model (SRSF2, albumin, TP53 score) that stratifies thrombocytopenic patients as low, intermediate, or high-risk with corresponding median survivals of 93.5, 29.5, and 7.2 months, respectively.

CONCLUSIONS

This study demonstrates that thrombocytopenia in MF is driven by different genetic mechanisms and is not uniformly high-risk. As novel agents with improved hematologic safety profiles enter the treatment landscape, thoughtful, risk-adapted therapeutic decisions will be required for MF patients with thrombocytopenia.

LAY SUMMARY

A significant minority of patients with myelofibrosis (MF) present with low platelets. Historically, these patients have been viewed as having "high-risk" disease, but this may not be uniformly true. Our study shows that there are various different causes for low platelets in MF, some of which represent high-risk disease whereas others do not. Additionally, our study shows that genetic mutations affecting the genes SRSF2 and TP53 are uniquely problematic in this group, as is a low serum albumin level. This study helps to risk-stratify MF patients with thrombocytopenia, thereby providing more information to guide informed and individualized treatment decisions.

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.

Momelotinib for the treatment of myelofibrosis with anemia

Myelofibrosis is a myeloproliferative neoplasm characterized by splenomegaly, debilitating constitutional symptoms and bone marrow failure. Disease-related anemia is common and associated with an inferior quality of life and survival. Unfortunately, few therapies exist to improve hemoglobin in myelofibrosis patients. Momelotinib is a JAK1/JAK2 inhibitor that also antagonizes ACVR1, leading to downregulation of hepcidin expression and increased availability of iron for erythropoiesis. In clinical testing, momelotinib has demonstrated a unique ability to improve hemoglobin and reduce transfusion burden in myelofibrosis patients with baseline anemia, while producing reductions in spleen size and symptom burden. This review explores the preclinical rationale, clinical trial data and future role of momelotinib in the evolving therapeutic landscape of myelofibrosis.

SOHO State of the Art Updates and Next Questions: Novel Therapies in Development for Myelofibrosis

Myeloproliferative neoplasms research has entered a dynamic and exciting era as we witness exponential growth of novel agents in advanced/early phase clinical trials for myelofibrosis (MF). Building on the success and pivotal role of ruxolitinib, many novel agents, spanning a wide range of mechanisms/targets (epigenetic regulation, apoptotic/intracellular signaling pathways, telomerase, bone marrow fibrosis) are in clinical development; several are studied in registrational trials and hold great potential to expand the therapeutic arsenal/shift the treatment paradigm if regulatory approval is granted. Insight into MF pathogenesis and its molecular underpinnings, preclinical studies demonstrating synergism of ruxolitinib with investigational agents, urgent unmet clinical needs (cytopenias, loss of response to JAK inhibitors); and progressive disease fueled the rapid rise of innovative therapeutics. New strategies include pairing ruxolitinib with erythroid maturation agents to manage anemia (luspatercept), designing rational combinations with ruxolitinib to boost responses in both the frontline and suboptimal response settings (pelabresib, navitoclax, parsaclisib), treatment with non-JAK inhibitor monotherapy in the second-line setting (navtemadlin, imetelstat), novel JAK inhibitors tailored to subgroups with challenging unmet needs (momelotinib and pacritinib for anemia and thrombocytopenia, respectively); and agents potentially enhancing longevity (imetelstat). Beyond typical endpoints evaluated in MF clinical trials (spleen volume reduction ≥ 35%, total symptom score reduction ≥ 50%) thus far, emerging endpoints include overall survival, progression-free survival, transfusion independence, anemia benefits, bone marrow fibrosis and driver mutation allele burden reduction. Novel biomarkers and additional clinical features are being sought to assess new agents and tailor emerging therapies to appropriate patients. New strategies are needed to optimize the design of clinical trials comparing novel combinations to standard agent monotherapy.

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.

OUP accepted manuscript

Background

This study analyses treatment patterns, health care resource utilization (HCRU), and costs in patients with myelofibrosis (MF) and a subgroup treated with ruxolitinib (RUX).

Materials and Methods

Treatment patterns, all-cause and MF-related HCRU, and costs were analyzed in adults with MF with continuous enrollment in a commercial or the Medicare Advantage health plan in the pre-index period, defined as the 12 months immediately prior to the index date (date of primary or secondary MF diagnosis), and the post-index period, defined as ≥6 months following the index date. In a subgroup analysis, outcomes were analyzed in patients treated with optimal RUX (OPT RUX, ≥30 mg) and suboptimal RUX (SUB RUX, <30 mg) in the pre-index RUX period, defined as the 3 months immediately prior to the index RUX date (first date for an RUX claim), and the post-index RUX period, defined as ≥6 months following the index RUX date.

Results

Of 2830 patients with an MF diagnosis, 1191 met eligibility requirements. The median age of patients was 72 years, 54% were male, and comorbidities were frequent. Sixty percent of patients received ≥1 line of therapy (LOT), of which 46% (n = 331) had ≥2 LOTs during the post-index MF period. Costs increased considerably 6-month pre-index to 6-month post-index (all-cause: cause ($24,216 to $48,966) and MF-related ($16,502 to $39,383), driven by inpatient stays and pharmacy costs. In the subgroup analysis, patients treated with RUX (n = 495) experienced significant disease burden and high costs, regardless of dose. A shorter duration of therapy and a higher rate of discontinuation were observed in patients treated with SUB RUX (n = 191) versus OPT RUX (n = 304).

Conclusion

These findings suggest a significant disease and economic impacts associated with MF patients that persists with RUX therapy, highlighting the need for additional therapeutic options for MF.

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.

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.

Novel therapeutics and targets in myelofibrosis

Myelofibrosis is a myeloproliferative neoplasm characterized by clonal proliferation of myeloid cells, bone marrow fibrosis and cytopenias, extramedullary hematopoiesis and hepatosplenomegaly, increased pro-inflammatory cytokine production, and systemic symptoms. Patients with MF also have a propensity toward leukemic transformation. Allogeneic hematopoietic stem cell transplantation (aHCT) is the only curative therapy for patients with MF; however, transplant-related morbidity and mortality precludes this option for the majority of patients. In the last decade, two targeted therapies have been approved for the treatment of MF, both JAK2 inhibitors, ruxolitinib and fedratinib. Despite the clinical efficacy of these two compounds in terms of splenomegaly and symptom burden reduction, there remain many areas of unmet need in the treatment of myelofibrosis. In this review, we discuss the limitations of currently approved treatment options and novel therapeutic targets with drug candidates in late-stage (phase II or III) clinical development for the treatment of MF. We delve into the mechanism of action and scientific rational of each candidate agent as well as the available clinical data, and ongoing trials that could lead to the approval of some of these novel therapies.

Next Generation Therapeutics for the Treatment of Myelofibrosis

Myelofibrosis is a myeloproliferative neoplasm characterized by splenomegaly, constitutional symptoms, bone marrow fibrosis, and a propensity towards transformation to acute leukemia. JAK inhibitors are the only approved therapy for myelofibrosis and have been successful in reducing spleen and symptom burden. However, they do not significantly impact disease progression and many patients are ineligible due to coexisting cytopenias. Patients who are refractory to JAK inhibition also have a dismal survival. Therefore, non-JAK inhibitor-based therapies are being explored in pre-clinical and clinical settings. In this review, we discuss novel treatments in development for myelofibrosis with targets outside of the JAK-STAT pathway. We focus on the mechanism, preclinical rationale, and available clinical efficacy and safety information of relevant agents including those that target apoptosis (navitoclax, KRT-232, LCL-161, imetelstat), epigenetic modulation (CPI-0610, bomedemstat), the bone marrow microenvironment (PRM-151, AVID-200, alisertib), signal transduction pathways (parsaclisib), and miscellaneous agents (tagraxofusp. luspatercept). We also provide commentary on the future of therapeutic development in myelofibrosis.

New germline GATA1 variant in females with anemia and thrombocytopenia

Familial forms of bone marrow defects are rare disorders and description of new cases are valuable opportunities to clarify the molecular machinery that triggers hematopoiesis and blood formation, as well as risk to malignant transformation. We investigated the genetic scenario and possible patterns of transmission in a rare case of familial myeloid disorder with a history of exposure to pesticides. Blood counts of two proband sisters, age 41 and 42, revealed mild anemia, neutrophilia and thrombocytopenia with bone marrow finding mimicking primary myelofibrosis in the cellular phase. We analyzed the coding regions of 78 myeloid neoplasms-related genes and 16 encoding xenobiotic metabolizing genes using Next-Generation Sequencing. The GATA1 variant c.788C > T, p.T263M, located in the C-terminal zinc finger domain of GATA1, was detected in the DNA of the two sisters. The screening of the other kindreds also revealed the p.T263M variant in the mother and two daughters with the same bone marrow disorder. This is the first report of an alteration in the GATA1 CF domain causing anemia, thrombocytopenia and megakaryocyte proliferation with mild myelofibrosis, correlating a new GATA1 germline variant with myeloid disorder.

Pacritinib demonstrates spleen volume reduction in patients with myelofibrosis independent of JAK2V617F allele burden

Myelofibrosis (MF) has heterogeneous clinical manifestations, with some patients exhibiting a myelodepletive phenotype characterized by cytopenias and an absent or low JAK2V617F allele burden. Ruxolitinib may be less effective in these patients. We assessed the efficacy of pacritinib, a JAK2/IRAK1 inhibitor, in MF patients with low JAK2V617F allele burden. In this post hoc analysis of the PERSIST-1 and -2 trials, patients with MF randomized to pacritinib or best available therapy (BAT) were stratified by JAK2V617F allele burden quartile for spleen response of ≥35% and improvement in total symptom score of ≥50%. Five hundred thirty-six patients were included. Patients with lower JAK2V617F allele burden had smaller baseline spleens and lower hemoglobin and platelet counts as compared with higher allele burden patients. Among pacritinib-treated patients, spleen responses were observed across all JAK2V617F allele burden quartiles and in JAK2V617F- disease. No spleen responses were observed among BAT-treated patients with allele burden ≤50% or JAK2V617F- disease. The intention-to-treat response rate was significantly higher on the pacritinib arm for JAK2V617F- disease (23.0% vs 0%; P = .033), and for the lowest allele burden quartiles (0%-25%: 20.9% vs 0%, P < .001; 25%-50%: 15.4% vs 0%, P = .020). There were significantly more symptom responders with pacritinib vs BAT in the 0% to 25% and 25% to 50% cohorts. Pacritinib treatment led to superior spleen and symptom burden reduction compared with BAT in patients with absent or low JAK2V617F allele burden, suggesting that pacritinib may be uniquely suited for patients with myelodepletive MF.

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.

Current and future therapies for myelofibrosis

Myelofibrosis is classified as a 'Philadelphia-chromosome negative' clonal myeloproliferative disorder. The heterogeneity of this condition and patient population and array of often challenging clinical manifestations can frequently make therapeutic decisions challenging. Despite many advances in therapy with targeted and combination approaches, following an enhanced understanding of underlying disease pathogenesis, cure only remains achievable with allogeneic stem cell transplant. This option is often limited to a small group of younger transplant-eligible patients with more advanced disease who have both a suitable donor and no or few co-morbidities. In this article, we will discuss up-to-date disease prognostication, common clinical challenges associated with myelofibrosis and both standard and novel therapeutic approaches. Increasingly complex prognostic modelling utilises patient-specific, haematological and genomic parameters to improve the accuracy of risk assessment and predict disease progression. We will also focus on difficult clinical scenarios such as disease-associated anaemia, thrombocytopenia and extremes of age. Future and evolving therapies within this field are highly anticipated and novel JAK inhibitor and non-JAK inhibitor-based therapy will also be discussed, including the new challenge of how to switch from one JAK inhibitor therapy to another.

Modern management of splenomegaly in patients with myelofibrosis

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm which can lead to massive splenomegaly secondary to extramedullary hematopoiesis. Patients frequently exhibit debilitating symptoms including pain and early satiety, in addition to cellular sequestration causing severe cytopenias. JAK 1/2 inhibitors, such as ruxolitinib and fedratinib, are the mainstay of therapy and produce significant and durable reductions in spleen volume. However, many patients are not eligible for JAK 2 inhibitor therapy or become refractory to treatment over time. Novel therapies are in development that can reduce the degree of splenomegaly for some of these patients. However, splenectomy, splenic irradiation, and partial splenic artery embolization remain valuable therapeutic options in select patients. In this review, we will discuss currently available pharmacologic therapies and describe promising drugs currently in development. We will also delve into the efficacy and safety concerns of splenectomy, splenic irradiation, and partial splenic artery embolization. Finally, we will propose a treatment algorithm to help guide clinicians in the management of symptomatic splenomegaly in patients with MF.

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.