Guideline for the diagnosis and management of myelofibrosis

Indication and management of allogeneic stem cell transplantation in primary myelofibrosis: a consensus process by an EBMT/ELN international working group

The aim of this work is to produce recommendations on the management of allogeneic stem cell transplantation (allo-SCT) in primary myelofibrosis (PMF). A comprehensive systematic review of articles released from 1999 to 2015 (January) was used as a source of scientific evidence. Recommendations were produced using a Delphi process involving a panel of 23 experts appointed by the European LeukemiaNet and European Blood and Marrow Transplantation Group. Key questions included patient selection, donor selection, pre-transplant management, conditioning regimen, post-transplant management, prevention and management of relapse after transplant. Patients with intermediate-2- or high-risk disease and age <70 years should be considered as candidates for allo-SCT. Patients with intermediate-1-risk disease and age <65 years should be considered as candidates if they present with either refractory, transfusion-dependent anemia, or a percentage of blasts in peripheral blood (PB) >2%, or adverse cytogenetics. Pre-transplant splenectomy should be decided on a case by case basis. Patients with intermediate-2- or high-risk disease lacking an human leukocyte antigen (HLA)-matched sibling or unrelated donor, should be enrolled in a protocol using HLA non-identical donors. PB was considered the most appropriate source of hematopoietic stem cells for HLA-matched sibling and unrelated donor transplants. The optimal intensity of the conditioning regimen still needs to be defined. Strategies such as discontinuation of immune-suppressive drugs, donor lymphocyte infusion or both were deemed appropriate to avoid clinical relapse. In conclusion, we provided consensus-based recommendations aimed to optimize allo-SCT in PMF. Unmet clinical needs were highlighted.

Clinical potential of pacritinib in the treatment of myelofibrosis

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

How We Treat Myeloproliferative Neoplasms

The present report focuses on management strategies for the myeloproliferative neoplasm according to the structure and processes we use within our center, a large tertiary unit in central London. The standard procedures for achieving an accurate diagnosis and risk stratification and therapeutic strategies for these diseases with a detailed focus on contentious areas are discussed. In the 9 years after the description of the Janus kinase 2 mutation, this field has altered quite radically in several aspects. For example, a new therapeutic paradigm exists, especially for myelofibrosis. We share how our unit has adapted to these changes.

Critical appraisal of the role of ruxolitinib in myeloproliferative neoplasm-associated myelofibrosis

The recent approval of molecular-targeted therapies for myeloproliferative neoplasm-associated myelofibrosis (MPN-MF) has dramatically changed its therapeutic landscape. Ruxolitinib, a JAK1/JAK2 tyrosine kinase inhibitor, is now widely used for first- and second-line therapy in persons with MPN-MF, especially those with disease-related splenomegaly, intermediate- or high-risk disease, and constitutional symptoms. The goal of this work is to critically analyze data supporting use of ruxolitinib in the clinical settings approved by the US Food and Drug Administration (FDA) and European Medicines Agency (EMA). We systematically reviewed the literature and analyzed the risk of biases in the two randomized studies (COMFORT I and COMFORT II) on which FDA and EMA approval was based. Our strategy was to apply the Grading of Recommendation, Assessment, Development and Evaluation (GRADE) approach by evaluating five dimensions of evidence: (1) overall risk of bias, (2) imprecision, (3) inconsistency, (4) indirectness, and (5) publication bias. Based on these criteria, we downgraded the evidence from the COMFORT I and COMFORT II trials for performance, attrition, and publication bias. In the disease-associated splenomegaly sphere, we upgraded the quality of evidence because of large effect size but downgraded it because of comparator choice and outcome indirectness (quality of evidence, low). In the sphere of treating persons with intermediate- or high-risk disease, we downgraded the evidence because of imprecision in effect size measurement and population indirectness. In the sphere of disease-associated symptoms, we upgraded the evidence because of the large effect size, but downgraded it because of comparator indirectness (quality of evidence, moderate). In conclusion, using the GRADE technique, we identified factors affecting the quality of evidence that were otherwise unstated. Identifying and evaluating these factors should influence the confidence with which physicians use ruxolitinib in persons with MPN-MF.

Limitations of fibrosis grade as diagnostic criteria for post polycythemia vera and essential thrombocytosis myelofibrosis

BACKGROUND

The clinical phenotype of patients with myeloproliferative neoplasms (MPNs) including primary myelofibrosis (PMF), polycythemia vera (PV), and essential thrombocytosis (ET) whom manifest WHO grade 1 marrow fibrosis is poorly defined. Current IWG-MRT criteria require 2+ marrow fibrosis for diagnosis of post PV/ET myelofibrosis (MF). In contrast, the 2008 WHO definition of PMF does not require a minimum fibrosis threshold.

METHODS

We retrospectively analyzed the clinical characteristics of 91 MPN patients with 1+ marrow fibrosis. We compared the clinical phenotype of sub threshold fibrosis PV/ET with that manifested by PMF. We applied the IWG-MRT criteria for post-PV/ET MF with the fibrosis component omitted and evaluated for percentage of criteria fulfillment.

RESULTS

When IWG-MRT criteria were applied to the PV/ET group, 38/58 (66%) of patients fulfilled criteria for diagnosis of post-PV/ET myelofibrosis except for the 2+ fibrosis requirement. Comparison of sub threshold fibrotic PV/ET clinical phenotype to PMF revealed similar characteristics including heavy symptomatic burden (57% and 52%), presence of splenomegaly (43% and 55%), leukoerythroblastic blood smear (38% and 45%), and median hemoglobin (12.8g/dL and 11.1g/dL).

CONCLUSION

MPN progression represents a biological spectrum and definitions of progression in ET/PV may benefit from criteria not restricted by degree of fibrosis.

Myelofibrosis patients in Belgium: disease characteristics

OBJECTIVE

To date, only a small number of epidemiological studies on myelofibrosis have been performed. The current study aimed to characterize the myelofibrosis patient population in Belgium according to pre-defined disease parameters (diagnosis, risk categories, hemoglobin <10 g/dl, spleen size, constitutional symptoms, platelet count, myeloblast count), with a view to obtaining a deeper understanding of the proportion of patients that may benefit from the novel myelofibrosis therapeutic strategies.

METHODS

A survey was used to collect data on prevalence and disease parameters on all myelofibrosis patients seen at each of 18 participating hematologic centers in 2011. Aggregated data from all centers were used for analysis. Analyses were descriptive and quantitative.

RESULTS

A total of 250 patients with myelofibrosis were captured; of these, 136 (54%) were male and 153 (61%) were over 65 years old. One hundred sixty-five (66%) of myelofibrosis patients had primary myelofibrosis and 85 (34%) had secondary myelofibrosis. One hundred ninety-three myelofibrosis patients (77%) had a palpable spleen. About a third of patients (34%) suffered from constitutional symptoms. Two hundred twenty-two (89%) myelofibrosis patients had platelet count ≧50 000/μl and 201 (80%) had platelet count ≧100 000/μl. Of 250 patients, 85 (34%) had a myeloblast count ≧1%. Six (2%) patients had undergone a splenectomy. Thirteen (5·2%) patients had undergone radiotherapy for splenomegaly.

CONCLUSIONS

The results of this survey provide insight into the characteristics of the Belgian myelofibrosis population. They also suggest that a large proportion of these patients could stand to benefit from the therapies currently under development.

Medical complications, resource utilization and costs in patients with myelofibrosis by frequency of blood transfusion and iron chelation therapy

Iron chelation therapies (ICTs) can help eliminate iron surplus in erythrocyte transfusion-dependent (TD) patients with myelofibrosis (MF). The study assessed adjusted incidence rate ratios (aIRRs) of MF-related complications and resource utilization (RU) and adjusted mean monthly inpatient cost differences in patients with TD MF treated with versus without ICT (ICT+ vs. ICT-) using data from two healthcare claims databases. Patients with ≥ 2 MF International Classification of Diseases, 9th Revision (ICD-9) diagnosis codes ≥ 30 days apart were included. Among 571 patients with TD MF, 103 (18%) were ICT+ and 468 (82%) were ICT-. ICT+ patients had lower rates of thrombocytopenia (aIRR: 0.55; p < 0.001), pancytopenia (0.53; p < 0.001), emergency room visits (0.84 [95% confidence interval: 0.74-0.96]) and inpatient stays (0.75 [0.64-0.87]), but higher rates of outpatient visits (1.21 [1.18-1.23]). Adjusted mean complication-related inpatient cost difference per month was lower in ICT+ patients (-$1804 [$570]; p = 0.004). ICT+ patients had significantly lower rates of acute care, but higher rates of outpatient care.

Update in the myeloproliferative neoplasms

The differential diagnosis of haematological abnormalities, such as leucocytosis, erythocytosis, thrombocytosis or indeed anaemia, is wide and disarming. Here we report on significant updates in the differential diagnosis of erythrocyosis and thrombocytosis presenting a simplified schema for the clinician. We then move to discuss significant advances in this field which have followed a series of key molecular findings, most specifically those affecting the JAK/STAT pathway.

How many JAK inhibitors in myelofibrosis?

The discovery of the activating mutation JAK2 V617F ushered a new era in MPN which included new diagnostic and prognostic criteria as well as a potential therapeutic target. JAK2 inhibition became a reality with first patients receiving drugs that targeted JAK2 in 2007 and was marked by the first approval in 2011 of Ruxolitinib a JAK 1 and 2-inhibitor to treat myelofibrosis (MF). In this article entitled "How many JAK inhibitors for myelofibrosis" we discuss JAK2 as a target, review briefly the benefits to patients with MF of JAK inhibition and highlight some of the differences between the number of JAK inhibitors currently being evaluated. Reflecting upon what we have learnt from the chronic myeloid leukaemia field and for MF regarding disease complexity as well as individual patient factors including resistance we discuss why it is likely we will need several different agents with JAK inhibitory activity. The next chapter discusses combination therapies for myelofibrosis which is a logical step in both trying to cure this disease and improve patient outcome and toxicities with JAK inhibitors.

Acute duodenal ischemia and periampullary intramural hematoma after an uneventful endoscopic retrograde cholangiopancreatography in a patient with primary myelofibrosis

Acute duodenal ischemia and periampullary intramural hematoma are rare complications after endoscopic retrograde cholangiopancreatography (ERCP). A 77-year-old man with splenomegaly complained of abdominal pain caused by common bile duct (CBD) stone. After successful removal of the CBD stone without immediate complications, the patient developed intramural hematoma around the ampulla of Vater along with diffuse duodenal edema. The findings were compatible with acute intestinal ischemia, and further evaluation revealed that he had underlying primary myelofibrosis. Myeloproliferative diseases are known to be significantly associated with an increased risk of thrombohemorrhagic complications. Therefore, particular attention should be given to this group of patients when a high-risk procedure such as ERCP is performed.

How common are myeloproliferative neoplasms? A systematic review and meta-analysis

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of diseases including polycythemia vera (PV), essential thrombocythemia (ET), and primary(idiopathic) myelofibrosis (PMF). In this systematic review, we provide a comprehensive report on the incidence and prevalence of MPNs across the globe. Electronic databases (PubMed, EMBASE, MEDLINE, and Web of Science) were searched from their inception to August 2012 for articles reporting MPN incidence or prevalence rates. A random effects meta-analysis was undertaken to produce combined incidence rates for PV, ET, and PMF. Both heterogeneity and small study bias were assessed. Thirty-four studies were included. Reported annual incidence rates ranged from 0.01 to 2.61, 0.21 to 2.27, and 0.22 to 0.99 per 100,000 for PV, ET, and PMF, respectively. The combined annual incidence rates for PV, ET, and PMF were 0.84, 1.03, and 0.47 per 100,000. There was high heterogeneity across disease entities (I(2) 97.1-99.8%) and evidence of publication bias for ET and PMF (Egger test, P = 50.007 and P ≤ 0.001, respectively).The pooled incidence reflects the rarity of MPNs. The calculated pooled incidence rates do not reflect MPN incidence across the globe due to the high unexplained heterogeneity. Improved, widespread registration of MPNs would provide better information for global comparison of the incidence and prevalence of MPNs.

Use of the Functional Assessment of Cancer Therapy--anemia in persons with myeloproliferative neoplasm-associated myelofibrosis and anemia

BACKGROUND

Anemia is common in myeloproliferative neoplasm (MPN)-associated myelofibrosis. The Functional Assessment of Cancer Therapy (FACT) measurement system is a patient-reported outcomes instrument that documents symptoms of the diverse aspects of cancer treatment. One FACT version, FACT-Anemia (FACT-An), documents symptoms of anemia related to cancer. The FACT-An has been validated in diverse cancer populations, but not in MPN-associated myelofibrosis.

OBJECTIVE

Our aim was to evaluate the relationship between anemia response to therapy with pomalidomide with or without corticosteroids and patient-reported outcomes using the FACT-An instrument.

METHODS

Data were obtained from a Phase II, randomized, double-blind Bayesian pick-the-winner trial of prednisone and pomalidomide in patients with MPN-associated myelofibrosis and anemia (red blood cell-transfusion dependence). Details of the study, including definitions of anemia, anemia response, red blood cell-transfusion, red blood cell-transfusion dependence, and red blood cell-transfusion independence, are reported. Change in quality of life from randomization to the last cycle of therapy was evaluated using the FACT-An Physical Well Being, Functional Well Being, Trial Outcome Index, and Anemia domains. Clinically important differences were used to determine the smallest difference in scores that patients perceived as beneficial in the FACT-An domains of interest. Patients were classified as meeting clinically important differences for responsiveness if their change score from baseline was >1 SEM, indicating improvement.

RESULTS

Eighty-five patients were studied. Thirty-one patients (37%) were classified as anemia responders by prospectively defined criteria. Across all FACT-An domains, anemia responders showed greater improvement in Physical Well Being, Functional Well Being, and Trial Outcome Index scores than did nonresponders. This improvement began at the second 28-day cycle of therapy and was sustained.

CONCLUSIONS

We show a correlation between anemia response and improved quality of life measured by the FACT-An instrument in patients with MPN-associated myelofibrosis and anemia.

Morphologic and cytogenetic differences between post-polycythemic myelofibrosis and primary myelofibrosis in fibrotic stage

Polycythemia vera and primary myelofibrosis share a propensity to progress toward a myelofibrotic late stage with overlapping clinical characteristics. Bone marrow features potentially useful for distinguishing the two entities have not been thoroughly investigated and, currently, clinical history is used for purposes of disease classification. This study describes in detail the morphologic features of 23 cases of post-polycythemic myelofibrosis and 15 cases of primary myelofibrosis with a similar degree of fibrosis, from two large medical centers. Cytogenetic results were available in 19 post-polycythemic myelofibrosis and in 13 primary myelofibrosis cases. JAK2 status and follow-up information was available in all cases. Cellularity was increased in both groups, but more so in post-polycythemic myelofibrosis than in primary myelofibrosis. In post-polycythemic myelofibrosis, most megakaryocytes retained polycythemia vera-like features including normally folded and/or hyperlobulated nuclei devoid of severe maturation defects; only in a few cases were rare tight clusters present. In primary myelofibrosis cases, megakaryocytes showed pronounced anomalies, including increased nuclear:cytoplasmic ratio, abnormal clumping of chromatin and frequent tight clustering. No differences in blast number (<1%) or in the myeloid:erythroid ratio were observed. Post-polycythemic myelofibrosis showed a higher degree of karyotypic alterations and higher percentage of cases with complex karyotype and/or two or more clones. Chromosome 1 defects were common in post-polycythemic myelofibrosis, whereas isolated del(20q) was the most common alteration in primary myelofibrosis. No survival differences were noted between the two groups. Post-polycythemic myelofibrosis cases retain a distinct megakaryocytic morphology that represents a useful clue for differential diagnosis. In addition, they more often display a complex karyotype than do primary myelofibrosis cases. These results suggest that myelofibrosis in polycythemia vera represents a form of progression characterized by profound genetic damage whereas in primary myelofibrosis it is an intrinsic part of the phenotypic manifestation of the disease, not necessarily associated with adverse cytogenetics.

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

BACKGROUND

Ruxolitinib, a Janus kinase 1 and 2 inhibitor, demonstrated improvements in spleen volume, symptoms, and survival over placebo and best available therapy in intermediate-2 or high-risk myelofibrosis patients with baseline platelet counts ≥100 × 109/L in phase III studies. The most common adverse events were dose-dependent anemia and thrombocytopenia, which were anticipated because thrombopoietin and erythropoietin signal through JAK2. These events were manageable, rarely leading to treatment discontinuation. Because approximately one-quarter of MF patients have platelet counts <100 × 109/L consequent to their disease, ruxolitinib was evaluated in this subset of patients using lower initial doses. Interim results of a phase II study of ruxolitinib in myelofibrosis patients with baseline platelet counts of 50-100 × 109/L are reported.

METHODS

Ruxolitinib was initiated at a dose of 5 mg twice daily (BID), and doses could be increased by 5 mg once daily every 4 weeks to 10 mg BID if platelet counts remained adequate. Additional dosage increases required evidence of suboptimal efficacy. Assessments included measurement of spleen volume by MRI, MF symptoms by MF Symptom Assessment Form v2.0 Total Symptom Score [TSS]), Patient Global Impression of Change (PGIC); EORTC QLQ-C30, and safety/tolerability.

RESULTS

By week 24, 62% of patients achieved stable doses ≥10 mg BID. Median reductions in spleen volume and TSS were 24.2% and 43.8%, respectively. Thrombocytopenia necessitating dose reductions and dose interruptions occurred in 12 and 8 patients, respectively, and occurred mainly in patients with baseline platelet counts ≤75 × 109/L. Seven patients experienced platelet count increases ≥15 × 109/L. Mean hemoglobin levels remained stable over the treatment period. Two patients discontinued for adverse events: 1 for grade 4 retroperitoneal hemorrhage secondary to multiple and suspected pre-existing renal artery aneurysms and 1 for grade 4 thrombocytopenia.

CONCLUSIONS

Results suggest that a low starting dose of ruxolitinib with escalation to 10 mg BID may be appropriate in myelofibrosis patients with low platelet counts.

Practical management of patients with myelofibrosis receiving ruxolitinib

Myelofibrosis (MF) is characterized by bone marrow fibrosis, progressive anemia and extramedullary hematopoiesis, primarily manifested as splenomegaly. Patients also experience debilitating constitutional symptoms, including sequelae of splenomegaly, night sweats and fatigue. Ruxolitinib (INC424, INCB18424, Jakafi, Jakavi), a JAK1 and JAK2 inhibitor, was approved in November 2011 by the US FDA for the treatment of intermediate- or high-risk MF, and more recently in Europe and Canada for the treatment of MF-related splenomegaly or symptoms. These approvals were based on data from two randomized Phase III studies: COMFORT-I randomized against placebo, and COMFORT-II randomized against best available therapy. In these studies, ruxolitinib rapidly improved multiple disease manifestations of MF, reducing splenomegaly and improving quality of life of patients and potentially prolonging survival. However, as with other chemotherapies, ruxolitinib therapy is associated with some adverse events, such as anemia and thrombocytopenia. The aims of this article are to provide a brief overview of ruxolitinib therapy, to discuss some common adverse events associated with ruxolitinib therapy and to provide clinical management recommendations to maximize patients' benefit from ruxolitinib.

A case of mistaken identity: When lupus masquerades as primary myelofibrosis

Introduction:

Autoimmune myelofibrosis is an uncommon hematologic disease characterized by anemia, bone marrow myelofibrosis, and an autoimmune feature. Myelofibrosis is often associated with other conditions, including infections, nutritional/endocrine dysfunction, toxin/drug exposure, and connective tissue diseases, including scleroderma and systemic lupus erythematosus. Absence of clonal markers (JAK2) and heterogeneity of the symptoms often complicate the diagnosis.

Case presentation:

Here, we present two cases of systemic lupus erythematosus–induced autoimmune myelofibrosis. The first case is of a 36-year-old African American female with diagnosis of systemic lupus erythematosus at the age of 12 years. The second patient is a 44-year-old African American male with family history of systemic lupus erythematosus who developed anemia and constitutional symptoms later on. Both patients showed hypercellularity and fibrotic changes of the bone marrow. Moreover, mutational analysis showed that both patients were wild type for JAK2 (V617F and exon 12) and MPL (exon 10).

Conclusions:

These two cases illustrate that anemic patients with fibrotic changes in the bone marrow without other clinicopathologic features associated with primary myelofibrosis in the presence of clinical manifestations and history of an autoimmune disease should suggest an autoimmune myelofibrosis. These cases demonstrate that a good clinical history combined with molecular technologies and pathomorphologic criteria are helpful in distinguishing between primary myelofibrosis and a nonclonal myelofibrosis from an associated condition.

Establishing optimal quantitative-polymerase chain reaction assays for routine diagnosis and tracking of minimal residual disease in JAK2-V617F-associated myeloproliferative neoplasms: a joint European LeukemiaNet/MPN&MPNr-EuroNet (COST action BM0902) study

Reliable detection of JAK2-V617F is critical for accurate diagnosis of myeloproliferative neoplasms (MPNs); in addition, sensitive mutation-specific assays can be applied to monitor disease response. However, there has been no consistent approach to JAK2-V617F detection, with assays varying markedly in performance, affecting clinical utility. Therefore, we established a network of 12 laboratories from seven countries to systematically evaluate nine different DNA-based quantitative PCR (qPCR) assays, including those in widespread clinical use. Seven quality control rounds involving over 21 500 qPCR reactions were undertaken using centrally distributed cell line dilutions and plasmid controls. The two best-performing assays were tested on normal blood samples (n=100) to evaluate assay specificity, followed by analysis of serial samples from 28 patients transplanted for JAK2-V617F-positive disease. The most sensitive assay, which performed consistently across a range of qPCR platforms, predicted outcome following transplant, with the mutant allele detected a median of 22 weeks (range 6–85 weeks) before relapse. Four of seven patients achieved molecular remission following donor lymphocyte infusion, indicative of a graft vs MPN effect. This study has established a robust, reliable assay for sensitive JAK2-V617F detection, suitable for assessing response in clinical trials, predicting outcome and guiding management of patients undergoing allogeneic transplant.

JAK2 mutants (e.g., JAK2V617F) and their importance as drug targets in myeloproliferative neoplasms

The Janus kinase 2 (JAK2) mutant V617F and other JAK mutants are found in patients with myeloproliferative neoplasms and leukemias. Due to their involvement in neoplasia and inflammatory disorders, Janus kinases are promising targets for kinase inhibitor therapy. Several small-molecule compounds are evaluated in clinical trials for myelofibrosis, and ruxolitinib (INCB018424, Jakafi®) was the first Janus kinase inhibitor to receive clinical approval. In this review we provide an overview of JAK2V617F signaling and its inhibition by small-molecule kinase inhibitors. In addition, myeloproliferative neoplasms are discussed regarding the role of JAK2V617F and other mutant proteins of possible relevance. We further give an overview about treatment options with special emphasis on possible combination therapies.

Update on the treatment of Ph-negative myeloproliferative neoplasms

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

JAK2-V617F-induced MAPK activity is regulated by PI3K and acts synergistically with PI3K on the proliferation of JAK2-V617F-positive cells

The identification of a constitutively active JAK2 mutant, namely JAK2-V617F, was a milestone in the understanding of Philadelphia chromosome-negative myeloproliferative neoplasms. The JAK2-V617F mutation confers cytokine hypersensitivity, constitutive activation of the JAK-STAT pathway, and cytokine-independent growth. In this study we investigated the mechanism of JAK2-V617F-dependent signaling with a special focus on the activation of the MAPK pathway. We observed JAK2-V617F-dependent deregulated activation of the multi-site docking protein Gab1 as indicated by constitutive, PI3K-dependent membrane localization and tyrosine phosphorylation of Gab1. Furthermore, we demonstrate that PI3K signaling regulates MAPK activation in JAK2-V617F-positve cells. This cross-regulation of the MAPK pathway by PI3K affects JAK2-V617F-specific target gene induction, erythroid colony formation, and regulates proliferation of JAK2-V617F-positive patient cells in a synergistically manner.

Assessing efficacy in myelofibrosis treatment: a focus on JAK inhibition

Myelofibrosis (MF) is characterized by splenomegaly, anemia and a debilitating symptom burden (e.g., fatigue, night sweats, pruritus, bone and muscle pain, undesired weight loss). Moreover, these symptoms impair activities of daily living and quality of life. Until recently, there have been no approved therapies for MF, and management of MF has been predominantly palliative. Dysregulated JAK-STAT signaling is associated with the pathologic MF disease state. A novel class of therapies, the JAK inhibitors, offers the potential to abrogate this pathologic signaling pathway. In clinical trials of patients with intermediate- and high-risk MF, JAK inhibitors have demonstrated efficacy in reducing splenomegaly and MF-associated symptoms. Evidence from ruxolitinib trials also suggests that JAK inhibitors may improve survival outcomes.