Clinical and molecular characterisation of a prospectively collected cohort of children and adolescents with polycythemia vera

Ruxolitinib in a Child With JAK2 Exon 12 Mutant Polycythemia Vera

BACKGROUND

Polycythemia Vera (PV) is a well-defined disorder of erythroid hyperproliferation that can result in life-threatening thromboembolic and hemorrhagic events. It is most prevalent in adults and is caused by mutations in Janus Kinase 2 (JAK2). Predominantly, PV is caused by a JAK2V617F mutation on exon 14.

OBSERVATIONS

A rare case of PV in a 9-year-old, driven by an uncommon, p.Glu543_Asp544del, JAK2 exon 12 mutation. Despite management with phlebotomy, aspirin and hydroxyurea, the patient suffered a dural sinus venous thrombosis, prompting a change in therapy to Ruxolitinib.

CONCLUSIONS

This is the first description of the successful use of ruxolitnib to treat a pediatric patient with PV caused by a JAK2 exon 12 mutation.

Overview of Myeloproliferative Neoplasms: History, Pathogenesis, Diagnostic Criteria, and Complications

Myeloproliferative disorders are a group of diseases morphologically linked by terminal myeloid cell expansion that frequently evolve from one clinical phenotype to another and eventually progress to acute myeloid leukemia. Diagnostic criteria for the Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) have been established by the World Health Organization and they are recognized as blood cancers. MPNs have a complex and incompletely understood pathogenesis that includes systemic inflammation, clonal hematopoiesis, and constitutive activation of the JAK-STAT pathway. Complications, such as thrombosis and progression to overt forms of myelofibrosis and acute leukemia, contribute significantly to morbidity and mortality of patients with MPN.

Polycythaemia vera: molecular genetics, diagnostics and therapeutics

Polycythaemia vera is one of several classical myeloproliferative neoplasms that may occur in a juvenile onset or late-onset adult forms. It is linked to specific genetic mutations that cause a deleterious elevation in the patient's red cell mass. The discourse on genetics includes an exposé on the molecular biology of the disease and how a shared JAK2 V617F mutation can co-exist among three distinct neoplasms. Concepts of genetics and immunology help define the origin and behaviour of the disease: the tracking of allele burdens of mutations (genetic dosage), the timing or order of acquired mutations, the import of bystander mutations and the onco-inflammatory response; all theories are invoked to explain the progression of disease severity and potential transformational leukaemia. The World Health Organization's diagnostic criteria are accessed to focus on the subtleties of the Hb laboratories and sifting through the challenging listing of differential diagnoses that mimic PV, and our report includes an overview of manual and automated phlebotomy (erythrocytapheresis) procedures, enumerating their clinical indications, significance of temporary phlebotomy resistance and optimizing safety/ efficacy, quality and cost. Stratification of low and high-risk disease distinguishes when to commence chemo-cytoreductive therapy in the high-risk patient to prevent thrombotic complications. Drug resistance is circumvented by artfully switching drugs or using novel drug designs.

A pharmacokinetic evaluation of ropeginterferon alfa-2b in the treatment of polycythemia vera

INTRODUCTION

Polycythemia vera (PV) is a Philadelphia chromosome-negative chronic myeloproliferative neoplasm (MPN). A newly developed PV treatment option, ropeginterferon alfa-2b, contains recombinant human alfa monoisomer as an active ingredient, resulting in a novel pharmacologic profile and improved tolerability. Efficacy studies conclude remarkable long-term hematological response and sustained JAK2V617F allele burden reduction. Ropeginterferon alfa-2b compound has been approved for the treatment of polycythemia vera without symptomatic splenomegaly.

AREAS COVERED

Current clinical trials are investigating the role of ropeginterferon alfa-2b in the first-line setting of treatment for PV. The safety and efficacy results of completed trials are summarized in this review. Metabolic, pharmacokinetic issues are also discussed of ropeginterferon alfa-2b.

EXPERT OPINION

Ropeginterferon alfa-2b is a targeted therapeutic option in the treatment of PV, representing a significant improvement compared to conventional cytoreductive therapies. The single isomer entity of the recombinant human interferon alfa-2b and the mono-pegylation method imparts favorable properties to the compound. The use of ropeginterferon alfa-2b allows extended dosing interval, reduces side effects, and may increase the overall survival of PV patients by reducing the risk of progression to myelofibrosis or acute leukemia. Clinical data suggests that the compound may provide a disease-modifying option for PV patients with asymptomatic splenomegaly.

Myeloproliferative Neoplasms in Children and Adolescents and Thrombosis at Unusual Sites: The Role of Driver Mutations

Myeloproliferative neoplasms (MPNs) in childhood and adolescence are rare and seldom complicated by thrombosis. We describe 3 cases of thrombosis at unusual sites in young patients with MPNs. In the pediatric MPN population, unlike in adult MPNs, a clonal mutation is identifiable in only a minority of cases (22% to 26%). All 3 of these individuals had JAK2 mutations driving the disease process. A literature search identified 19 cases of MPN-associated thrombosis in children. Seventeen of the 19 children (89.5%) had a driver mutation. These cases suggest that identifiable driver mutations may confer an increased thrombotic risk in children with MPNs.

Ruxolitinib treatment in an infant with JAK2+ polycythaemia vera-associated Budd-Chiari syndrome

Budd-Chiari syndrome (BCS) is caused by hepatic venous outflow obstruction commonly seen with myeloproliferative neoplasms (MPNs). Polycythaemia vera (PV) is a very rare MPN in childhood. This is the youngest reported patient diagnosed with PV and BCS secondary to JAK V617F mutation.A 26-month-old girl was admitted with a 5-month history of abdominal distension, hepatosplenomegaly and ascites. Imaging studies revealed occlusion of the right hepatic vein and marked attenuation of the middle and left hepatic veins. BCS was diagnosed after excluding other causes of chronic liver disease. Mandatory prothrombotic workup revealed underlying PV.Partial recanalisation of hepatic veins occurred following anticoagulation therapy and PV was well controlled by pegylated interferon and hydroxycarbamide until she developed nephrotic syndrome, likely secondary to pegylated interferon. Therefore, treatment was modified to ruxolitinib, a novel-JAK-2 inhibitor; the therapy has been effective for almost 20 months with a good response and has no side effects.

Myeloproliferative Neoplasms in Children

Myeloproliferative neoplasms (MPN) are a group of clonal hematopoietic stem cell disorders characterized by aberrant proliferation of one or more myeloid lineages often with increased immature cells in the peripheral blood. The three classical BCR-ABL-negative MPNs are: 1) polycythemia vera (PV), 2) essential thrombocythemia (ET), and 3) primary myelofibrosis (PMF), which are typically disorders of older adults and are exceedingly rare in children. The diagnostic criteria for MPNs remain largely defined by clinical, laboratory and histopathology assessments in adults, but they have been applied to the pediatric population. The discovery of the JAK2 V617F mutation, and more recently, MPL and CALR mutations, are major landmarks in the understanding of MPNs. Nevertheless, they rarely occur in children, posing a significant diagnostic challenge given the lack of an objective, clonal marker. Therefore, in pediatric patients, the diagnosis must rely heavily on clinical and laboratory factors, and exclusion of secondary disorders to make an accurate diagnosis of MPN. This review focuses on the clinical presentation, diagnostic work up, differential diagnosis, treatment and prognosis of the classical BCR-ABL-negative MPNs (PV, ET and PMF) in children and highlights key differences to the adult diseases. Particular attention will be given to pediatric PMF, as it is the only disorder of this group that is observed in infants and young children, and in many ways appears to be a unique entity compared to adult PMF.

Erythrocytosis in children and adolescents-classification, characterization, and consensus recommendations for the diagnostic approach

During recent years, the increasing knowledge of genetic and physiological changes in polycythemia vera (PV) and of different types of congenital erythrocytosis has led to fundamental changes in recommendations for the diagnostic approach to patients with erythrocytosis. Although widely accepted for adult patients this approach may not be appropriate with regard to children and adolescents affected by erythrocytosis. The "congenital erythrocytosis" working group established within the framework of the MPN&MPNr-EuroNet (COST action BM0902) addressed this question in a consensus finding process and developed a specific algorithm for the diagnosis of erythrocytosis in childhood and adolescence which is presented here.

Mutations profile of polycythemia vera and essential thrombocythemia among Japanese children

BACKGROUND

Acquired somatic mutations of JAK2 have been reported to play a pivotal role in the pathogenesis of BCR-ABL1-negative myeloproliferative neoplasm (MPN). However, the molecular characteristics of childhood MPN remain to be elucidated.

PATIENT AND METHODS

We investigated a group of pediatric patients diagnosed either with essential thrombocythemia (ET; N = 9) or polycythemia vera (PV; N = 4) according to WHO criteria (median age = 10 years; range 1.5-15 years) in whom direct sequencing was performed for the existence of genetic alterations in JAK2, MPL, TET2, ASXL1, CBL, IDH1, and IDH2. More sensitive allele specific polymerase chain reaction was used for JAK2(V617F) genotyping.

RESULTS

We found three patients harbor JAK2(V617F) mutation (2/9 ET and 1/4 PV). Bone marrow examination showed small and large megakaryocytes with dysplastic features in JAK2(V617F)-positive ET patients compared to those without JAK2(V617F). We identified a previously unrecognized missense mutation at codon 1230 in exon 12 of ASXL1 gene in ET and PV patients (1/9 ET and 1/4 PV). Otherwise, no genetic alterations could be detected in JAK2 exon 12, MPL, TET2, CBL, IDH1, and IDH2 in all ET and PV patients.

CONCLUSION

Although JAK2 mutations in childhood ET and PV are not as frequent as reported in adult patients, JAK2 is the most frequently mutated gene in childhood MPN known so far. Owing to the presence of childhood MPN without any genetic alterations in JAK2, MPL, TET2, ASXL1, CBL, IDH1, and IDH2, new biological markers have to be found.

Dural sinus thrombosis owing to polycythaemia vera in a 12-year-old girl

Because of the rarity of dural sinus thrombosis in children with polycythaemia vera (PV), the options for diagnosis and treatment remain elusive. A 12-year-old girl was admitted with dural sinus thrombosis associated with PV, diagnosed by magnetic resonance venography. She was managed with interventional endovascular thrombolectomy and venoplasty, phlebotomy, hydroxyurea, low molecular weight heparin, and aspirin followed by warfarin. She made a good recovery without residual neurological deficit. This case highlights the importance of diagnosis and appropriate intervention with multi-modality treatments in patients with PV and thrombosis.

Thrombocythemia and polycythemia in patients younger than 20 years at diagnosis: clinical and biologic features, treatment, and long-term outcome

Sixty-four patients < 20 years of age, investigated for a suspicion of Philadelphia-negative myeloproliferative disease (MPD), were retrospectively evaluated to characterize the different forms and to examine the treatments used and long-term outcome. JAK2 mutations, endogenous erythroid colony growth, and clonality were investigated in 51 children. Mutations of thrombopoietin, the thrombopoietin receptor (MPL), and the erythropoietin receptor and mutations of other genes involved in the pathogenesis of MPD were investigated in JAK2 wild-type patients. Based on our criteria for childhood MPD, we identified 34 patients with sporadic thrombocythemia (ST), 16 with hereditary thrombocytosis (HT), 11 with sporadic polycythemia (SP), and 3 with hereditary polycythemia (HP). JAK2V617F mutations were present in 47.5% of ST and in no HT. The MPLS505A mutation was detected in 15/16 HT patients and in no ST (P < .00001). The JAK2V617F mutation occurred in 27% of SP patients diagnosed according to the Polycythemia Vera Study Group or World Health Organization 2001 criteria. Children with ST received more cytoreductive drugs than those with HT (P = .0006). After a median follow-up of 124 months, no patient had developed leukemia or myelofibrosis and 5% had thrombosis; the miscarriage rate in thrombocythemic patients was 14%. The low complication rate in our population suggests that children with MPD may be managed by tailored approaches.

The JAK2 exon 12 mutations: a comprehensive review

A variety of acquired mutations targeting JAK2 exon 12 are present in those patients with the myeloproliferative neoplasm, polycythemia vera, that lack the more common JAK2V617F mutation. Both mutation types perturb erythropoiesis, with individuals presenting with a raised hematocrit, reduced serum erythropoietin levels, and erythropoietin-independent erythroid progenitor cells. However, there are also phenotypic differences that, until recently, precluded a significant proportion of patients with a JAK2 exon 12 mutation from receiving an appropriate diagnosis. Here, we review the literature published on the JAK2 exon 12 mutations and compare the biology associated with these mutations with that of JAK2V617F.

Clinical and hematological presentation of children and adolescents with polycythemia vera

Polycythemia vera (PV) in children and adolescents is very rare. Data on clinical and laboratory evaluations as well as on treatment modalities are sparse. Here, we report the long-term clinical course of a PV patient first diagnosed more than 40 years ago at age 12. In addition, after a systematic review of the scientific medical literature, clinical and hematological data of 35 patients (19 female and 17 male) from 25 previous reports are summarized. Three patients developed PV following antecedent hematological malignancies. Budd-Chiari syndrome was diagnosed in seven patients indicating a particular risk of young patients of developing this disorder. One patient presented with ischemic stroke, one patient with gangrene, and three patients with severe hemorrhage. Three patients died from disease-related complications. Hematocrit levels and platelet counts were not correlated with disease severity. Leukocytosis >15 x 10(9)/L was present in 9/35 patients and associated with a thromboembolic or hemorrhagic complication in seven patients. The few available data on molecular genetics and endogenous erythroid colony growth indicate changes comparable to those detectable in adult patients. Treatment varied enormously. It included aspirin, phlebotomy, hydroxycarbamide, busulfan, melphalan, pyrimethamine, and interferon-alpha. Two patients successfully underwent stem cell transplantation. Currently, it is impossible to treat an individual pediatric PV patient with an evidence-based regimen.