Myeloproliferative neoplasms (MPNs) are a heterogeneous group of clonal diseases characterized by the excessive and chronic production of mature cells from one or several of the myeloid lineages. Recent advances in the biology of MPNs have greatly facilitated their molecular diagnosis since most patients present with mutation(s) in the JAK2, MPL, or CALR genes. Yet the roles played by these mutations in the pathogenesis and main complications of the different subtypes of MPNs are not fully elucidated. Importantly, chronic inflammation has long been associated with MPN disease and some of the symptoms and complications can be linked to inflammation. Moreover, the JAK inhibitor clinical trials showed that the reduction of symptoms linked to inflammation was beneficial to patients even in the absence of significant decrease in the JAK2‐V617F mutant load. These observations suggested that part of the inflammation observed in patients with JAK2‐mutated MPNs may not be the consequence of JAK2 mutation. The aim of this paper is to review the different aspects of inflammation in MPNs, the molecular mechanisms involved, the role of specific genetic defects, and the evidence that increased production of certain cytokines depends or not on MPN‐associated mutations, and to discuss possible nongenetic causes of inflammation.

Calreticulin (CALR) mutations have been reported in JAK2 and MPL-negative essential thrombocythemia and primary myelofibrosis. In contrast, no CALR mutations have ever been reported in the context of Polycythemia Vera (PV). Here, we describe two JAK2^V617F- JAK2^exon12-negative PV patients who presented with a CALR mutation in peripheral granulocytes at the time of diagnosis. In both cases, the CALR mutation was a 52 bp deletion. Single erythroid colonies (BFU-E) from one patient were grown in vitro and genotyped: the same CALR del 52 bp mutation was noted in 31 of the 37 colonies examined; 30/31 BFU-E were heterozygous for CALR del 52 bp, and 1/31 BFU-E was homozygous for CALR del 52 bp. In summary, although unknown mutations leading to PV cannot be ruled out, our results suggest that CALR mutations can be associated with JAK2-negative PV.

Since the discovery of the JAK2 V617F mutation in the majority of the myeloproliferative neoplasms (MPN) of polycythemia vera, essential thrombocythemia and primary myelofibrosis ten years ago, further MPN‐specific mutational events, notably in JAK2 exon 12, MPL exon 10 and CALR exon 9 have been identified. These discoveries have been rapidly incorporated into evolving molecular diagnostic algorithms. Whilst many of these mutations appear to have prognostic implications, establishing MPN diagnosis is of immediate clinical importance with selection, implementation and the continual evaluation of the appropriate laboratory methodology to achieve this diagnosis similarly vital. The advantages and limitations of these approaches in identifying and quantitating the common MPN‐associated mutations are considered herein with particular regard to their clinical utility. The evolution of molecular diagnostic applications and platforms has occurred in parallel with the discovery of MPN‐associated mutations, and it therefore appears likely that emerging technologies such as next‐generation sequencing and digital PCR will in the future play an increasing role in the molecular diagnosis of MPN.

Background Many different techniques have been designed for the quantification of JAK2V617F allelic burden, sometimes producing discrepant results. Design and Methods JAK2V617F quantification techniques were compared among 16 centers using 11 assays based on quantitative polymerase chain reaction (with mutation-specific primers or probes, or fluorescent resonance energy transfer/melting curve analysis), allele-specific polymerase chain reaction, conventional sequencing or pyrosequencing. Results A first series of blinded samples (granulocyte DNA, n=29) was analyzed. Seven assays (12 centers) reported values inside the mean±2SD; the mean coefficient of variation was 31%. Sequencing techniques lacked sensitivity, and strong discrepancies were observed with four techniques, which could be attributed to inadequate standards or to different modes of expression of results. Indeed, quantification of JAK2V617F in relation to another control gene produced higher than expected values, suggesting the possibility of more than two JAK2 copies/cell. After calibration of assays with common 1% to 100% JAK2V617F standards (dilutions of UKE-1 cells in normal leukocytes), 14 centers tested ten new samples. JAK2V617F allelic burdens greater or equal than 1% were then reliably quantified by five techniques – one allele specific-polymerase chain reaction and four TaqMan allele-specific quantitative polymerase chain reaction assays, including one previously giving results outside the mean±2SD – with a lower mean coefficient of variation (21%). Of these, only the two TaqMan allele-specific quantitative polymerase chain reaction assays with primer-based specificity could detect 0.2% JAK2V617F. Conclusions Techniques expressing the allelic burden as JAK2V617F/total JAK2 and using a common set of standards produced similar quantification results but with variable sensitivity. Calibration to a reference standard improved reproducibility.