CALR mutations are rare in childhood essential thrombocythemia

Clinical features of children with polycythemia vera, essential thrombocythemia, and primary myelofibrosis in Japan: A retrospective nationwide survey

Background

Philadelphia-negative (Ph-negative) myeloproliferative neoplasms (MPNs), including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are exceptionally rare during childhood. Thus, clinical features of pediatric Ph-negative MPNs remain largely unknown. This study was therefore performed to address this.

Methods

We performed a retrospective study to collect clinical information of children diagnosed with Ph-negative MPNs from 2000 to 2016 using questionnaires in qualified institutions in Japan. The results obtained from the questionnaire survey were then combined with those from the national registry data.

Results

Among 50 children identified, five had PV, 44 had ET, and one had PMF. Median age at diagnosis was 14.0, 9.0, and 0 years, respectively. Male to female ratio was 4:1, 21:23, and 1:0, respectively. Detection rates of the JAK2 V617F variant were 0/5 in PV and 9/39 in ET. Frequencies of complications, such as thrombosis and subsequent leukemia, were lower than complication frequencies in adults. We identified two children who developed subsequent leukemia, which has not been reported previously, and one of them died.

Conclusion

This is the first nationally representative survey of pediatric Ph-negative MPNs. Given its rarity, an international collaboration with comprehensive genetic analyses might be needed to fully elucidate the clinical and genetic features.

Contemporary management of essential thrombocythemia in children

INTRODUCTION

Essential thrombocythemia (ET) is a disease which is extremely rare in children. Only recently, data on pediatric ET have become available. Areas covered: In children with sustained platelet count over 450 x 10⁹/L, secondary thrombocytosis must be ruled out. ET workup comprehends research of JAK2V617F, CALR and MPL mutations and bone marrow biopsy (BM). In asymptomatic children wait and watch is the best option. Aspirin controls headache and other microvascular disturbances. Patients with venous thrombosis need anticoagulation. Cytoreductive drugs in children with ET should be prescribed as a last choice. Hydroxyurea and IFN-a are first-line therapy at any age including children; Anagrelide is not licensed as first-line therapy for ET in Europe. New JAK2-inhibitors are not clearly useful in ET and hence not approved for ET. Expert opinion: The most challenging problem is to understand if a child with prolonged not secondary thrombocytosis really has ET. Diagnostic workup requires molecular and histological studies. The rare children with clonal ET have features like those of adults. Patients with ET have long expected survival and the treatment in children must be long-term efficacious and well tolerated.

Characteristics and outcomes of patients with essential thrombocythemia or polycythemia vera diagnosed before 20 years of age: a systematic review

Although it is well known that myeloproliferative neoplasms occur in younger patients, few large cohorts of such patients have been reported. Thus, our knowledge about circumstances of diagnosis, outcome and treatment is limited, especially for children and young adults. We therefore performed a systematic review of cases, published since 2005, concerning patients aged below 20 years at the time of diagnosis of essential thrombocythemia or polycythemia vera. We identified 396 cases of essential thrombocythemia and 75 of polycythemia vera. The median age at diagnosis was 9.3 and 12 years, respectively, and females constituted 57.6% and 45% of the groups, respectively. Half of the patients were asymptomatic at diagnosis. The proportion of so-called triple negativity was high: 57% in essential thrombocythemia and 73% in polycythemia vera. The incidence of thrombosis during the follow-up was 9.3% in patients with polycythemia vera and less, 3.8%, in those with essential thrombocythemia. Venous events were predominant (84.2%), with hemorrhagic episodes being rarer (<5%). The risk of evolution also seemed low (2% to myelofibrosis and no reports of acute leukemia), but the median follow-up was only 50 months. Survival curves were not available. Half of the patients received an antithrombotic drug and 40.5% received a cytoreductive drug. All data should be analyzed with care because of the proportion of missing data (10.7% to 74.7%). This review highlights interesting points concerning this population of young patients with myeloproliferative neoplasms, including that such patients were identified as negative for all common driver mutations, but also shows the need for larger contemporary cohorts with longer follow-up to assess the true prognosis of these patients.

Clinical validation of a multipurpose assay for detection and genotyping of CALR mutations in myeloproliferative neoplasms

OBJECTIVES

To develop a polymerase chain reaction (PCR)-based approach to detect CALR mutations in myeloproliferative neoplasms (MPNs) in a clinical laboratory.

METHODS

DNA was extracted from bone marrow aspirate samples of 67 JAK2 wild-type MPNs (22 with matched peripheral blood), 54 cases of unclassifiable myelodysplastic syndrome/MPN, and 16 cases of atypical chronic myeloid leukemia. We used genomic DNA to detect somatic mutations in exon 9 of CALR and PCR with fluorescently labeled and M13-tagged primers and subjected the products to capillary electrophoresis (CE) followed by Sanger sequencing. Detailed assay performance characteristics were established.

RESULTS

We identified CALR mutations in 19 (28.4%) of 67 JAK2-negative MPNs, including 14 type I (52-base pair [bp] deletion), four type II (5-bp insertions), and one type III (18-bp deletion). All mutations were confirmed by Sanger sequencing. Sensitivity studies showed 2.5% and 5% mutation detection levels by CE and Sanger sequencing, respectively, with high reproducibility.

CONCLUSIONS

This assay allows for rapid, convenient screening for CALR mutations in MPNs, thereby reducing the number of cases that require assessment by Sanger sequencing, reducing labor and improving turnaround time.

Are all cases of paediatric essential thrombocythaemia really myeloproliferative neoplasms? Analysis of a large cohort

Sporadic essential thrombocythaemia (ET) is rare in paediatrics, and the diagnostic and clinical approach to paediatric cases cannot be simply copied from experience with adults. Here, we assessed 89 children with a clinical diagnosis of ET and found that 23 patients (25·8%) had a clonal disease. The JAK2 V617F mutation was identified in 14 children, 1 child had the MPL W515L mutation, and 6 had CALR mutations. The monoclonal X-chromosome inactivation pattern was seen in six patients (two with JAK2 V617F and two with CALR mutations). The other 66 patients (74·2%) had persistent thrombocytosis with no clonality. There were no clinical or haematological differences between the clonal and non-clonal patients. The relative proportion of ET-specific mutations in the clonal children was much the same as in adults. The higher prevalence of non-clonal cases suggests that some patients may not have myeloproliferative neoplasms, with significant implications for their treatment.

The molecular landscape of childhood myeloproliferative neoplasms

The classical myeloproliferative neoplasms (MPN) are comparatively uncommon in children and display a degree of mutational naivety if considering the high frequency of known MPN driver events observed in the corresponding adult diseases. Whole exome sequencing has unravelled much of the underlying molecular complexity of MPN in adult patients yet less is known of the pathogenetic mechanisms when these diseases occur in childhood. It is proposed that such methodological approaches will contribute significant insights into the molecular landscape of childhood MPN that may in turn impact on understanding the pathophysiology of disease in their adult counterparts.