Mutations in the gene for calreticulin (CALR) were identified in the myeloproliferative neoplasms (MPNs) essential thrombocythaemia (ET) and primary myelofibrosis (MF) in 2013; in combination with previously described mutations in JAK2 and MPL, driver mutations have now been described for the majority of MPN patients. In subsequent years, researchers have begun to unravel the mechanisms by which mutant CALR drives transformation and to understand their clinical implications. Mutant CALR activates the thrombopoietin receptor (MPL), causing constitutive activation of Janus kinase 2 (JAK2) signaling and cytokine independent growth in vitro. Mouse models show increased numbers of hematopoietic stem cells (HSCs) and overproduction of megakaryocytic lineage cells with associated thrombocytosis. In the clinic, detection of CALR mutations has been embedded in World Health Organization and other international diagnostic guidelines. Distinct clinical and laboratory associations of CALR mutations have been identified together with their prognostic significance, with CALR mutant patients showing increased overall survival. The discovery and subsequent study of CALR mutations have illuminated novel aspects of megakaryopoiesis and raised the possibility of new therapeutic approaches.

Introduction

In 2013, 2 seminal papers described mutations in the calreticulin gene (CALR) in a subset of essential thrombocythaemia (ET) or myelofibrosis (MF) patients^{1, 2}; more than 36 different mutations were reported, all of them insertions or deletions (indels) causing a +1 frameshift within exon 9 that generated a novel C-terminal sequence. These mutations were mutually exclusive with Janus kinase 2 (JAK2) and thrombopoietin receptor (MPL) mutations, found in the majority of ET and MF patients. The two most frequent CALR mutations, a 52 base pair (bp) deletion (DEL) and a 5 bp insertion (INS), accounted for 85% of the mutations and were termed type I and II, respectively (Fig. 1A). Apart from the two most common mutations, a myriad of other mutations have been identified. These less common mutations can be classified as either type I-like or type II-like based on predicted helical secondary structure³ or the number of calcium-binding amino acids remaining in the novel C-terminus.⁴

While previously identified phenotypic driver mutations in MPNs affect genes directly involved in cytokine signaling or its regulation (eg, BCR-ABL1,⁵ CSF3R,⁶ JAK2,^7-10 MPL ^{11, 12}), CALR instead encodes an endoplasmic reticulum (ER) chaperone that serves multiple functions, including calcium homeostasis and glycoprotein quality control, and is distributed across different cellular compartments.¹³ CALR is encoded by a highly developmentally conserved gene, with 70% nucleotide homology between mouse and human, and has three domains: an N-terminal lectin domain (N), a proline-rich domain (P), and an acidic carboxyl terminus (C) that terminates in the amino acid sequence KDEL, an ER retrieval signal.¹⁴ The N domain of CALR is primarily responsible for its chaperone activity, while its C domain has been identified as the major binding site of calcium in the ER, binding Ca²⁺ ions with high capacity and low affinity.¹⁵ Because no truncating mutations were found in the original patient cohorts, a gain-of-function mechanism for CALR mutations was postulated.¹⁶

Details are in the caption following the image — **Figure 1**
Open in figure viewer PowerPoint

**A. Native and type I and type II-mutant CALR primary sequence**. The frameshift (frameshifted amino acid residues in bold) within the exon 9 generates a common novel CT in cyan, which is common to all frameshift mutations and substitutes most of the native C domain, involved in the storage of calcium. The ER retrieval signal (KDEL) is also lost. Adapted from Nangalia et al.² B. Distribution of driver mutations in MPN. TN stands for triple negative, that is, neither *JAK2*, *CALR,* nor *MPL* mutated. Adapted from Klampfl et al.¹

Over the past 6 years, extensive work has begun to unravel the mechanisms underlying mutant CALR-driven transformation in cellular systems and animal models. Clinical investigations have started to tease out differences between CALR-positive and negative MPNs as well as between type I and type II CALR mutations. Finally, advances in the understanding of the pathogenesis of CALR-driven MPNs are paving the way for a more tailored treatment regimen for CALR-mutated patients.

Consequences of CALR mutation

Functions of mutant CALR in vitro

CALR mutations are associated with ET and MF, as are JAK2 and MPL mutations, but are mutually exclusive with JAK2 and MPL, suggesting they drive transformation through the same pathway (some reports have found rare patients with co-occurring JAK2 V617F and CALR mutations, but they did not address the possibility of biclonality^17-19). Consistent with this finding, initial experiments showed that all of these mutations operate through the constitutive activation of the JAK2 signaling cascade.^{1, 2} Much of the research to date on the oncogenic effects of CALR mutations has focused on MPL signaling in cytokine-dependent cellular systems. CALR mutations require the expression of MPL to render autonomous cell growth in Ba/F3 cells,^20-22 UT-7/TPO cells^{20, 23} and γ2A cells expressing JAK2.²⁴ Conversely, mutant CALR is unable to induce cytokine independence when co-expressed with erythropoietin receptor (EPOR)^{20, 24} and drives little²⁴ or no²⁰ autonomous cell growth upon co-expression with the granulocyte-colony stimulating factor receptor (CSF3R). The lack of activation of EPOR by mutant CALR likely explains why CALR mutations are not seen in polycythemia vera (PV) patients (Fig. 1B, Fig. 2).

In order for mutant CALR to drive transformation, the presence of the extracellular domain of MPL is required,^{24, 25} particularly its sites for N-linked glycosylation,²⁴ where a lectin such as CALR would be predicted to bind. Indeed, the glycan-binding sites of CALR itself are crucial for activating MPL,²⁴ while the polypeptide-binding regions and chaperone activity of CALR are dispensable.²⁵ Mutant CALR also requires its novel positively charged C-terminal residues to activate MPL signaling: mutation of these residues to uncharged glycine residues abrogates its transforming ability.²⁰ Of note, truncation of exon 9 eliminates the transforming abilities of mutant CALR, further underscoring the functional importance of the novel C-terminus.²⁴ Analogously, removal of the 36 most distal residues from the new C-terminus prevents mutant CALR from transforming Ba/F3-MPL cells. This Δ36 mutant is still able to bind to MPL, suggesting that binding to and activation of the receptor may be two separate processes.²⁵ In order to activate MPL, mutant CALR must oligomerize²⁶; oligomerization of wild-type CALR has also been observed when CALR is N-arginylated,²⁷ though the N-arginylation status of mutant CALR is unknown. Mutant CALR can only activate MPL and drive STAT5 activity at the cell surface: if the complex is retained in the ER via treatment with Brefeldin A, an inhibitor of ER-Golgi trafficking, no STAT5 transcriptional activity is observed. Additionally, mutant CALR can rescue the cell surface trafficking of a MPL mutant, MPL R102P, that is normally retained in the ER in some cases of hereditary thrombocytosis.²⁸

Most work on mutant CALR has focused on human CALR and MPL, but there is some evidence that analogous frameshift mutations in murine Calr can transform γ2A and Ba/F3 cells when co-expressed with either human MPL or CSF3R.^{20, 29} While the majority of studies on signaling pathways driven by mutant CALR have used well-established cell lines, one study generated induced pluripotent stem cell-derived hematopoietic progenitor cell lines from a healthy donor and a patient with a type II CALR mutation. Here, mutant CALR increased megakaryocyte numbers with premature commitment to megakaryopoiesis.³⁰ Cell lines derived from patients bearing disease-associated mutations may thus represent promising lines of research in the future.

Though constitutive activation of the JAK2 signaling cascade is considered the primary mechanism driving the effects of CALR mutations, other potential mechanisms have been investigated. CALR and JAK2 mutations overlap to some extent in their ability to activate JAK-STAT signalling³¹; however, additional mechanisms may contribute to mutant CALR-driven oncogenesis.³² CALR mutations lead to the replacement of a series of Ca²⁺-binding, negatively charged amino acids with a stretch of positively charged residues. This would perturb the ability of CALR to properly retain Ca²⁺ ions within the ER lumen, affecting Ca²⁺ signaling pathways. Consistent with this idea, megakaryocytes derived from type I CALR-mutated patients showed an enhanced release of Ca²⁺ from ER stores compared to those derived from either healthy donors or type II mutated patients.⁴ This enhanced Ca²⁺ signaling has been attributed to the process of store-operated calcium entry (SOCE), which is normally mediated by the ER Ca²⁺ sensor STIM1. The presence of mutant CALR destabilizes a complex between CALR, ERp57, and STIM1, leading to increased SOCE and thus cell proliferation.³³ Ca²⁺ signaling has also been shown to regulate megakaryocyte function³⁴ and could therefore contribute to phenotypic differences between distinct types of CALR mutations, as discussed further below.

It is difficult to predict whether C-terminal mutations would have a significant structural effect on CALR as they are in a region with a great degree of plasticity³⁵; most structural studies of CALR to date have focused on the more structured N-terminal regions of the protein.³⁶ Structural modeling analysis predicts that the C-terminus is intrinsically disordered in both wild-type and mutant contexts.³⁷ Another consequence of CALR frameshift mutations is the loss of the C-terminal KDEL sequence, typically responsible for ER retrieval, resulting in a shift to ER-Golgi intermediate and Golgi compartments compared to WT CALR.²⁴ Mislocalized mutant CALR could therefore produce ectopic effects. For instance, a recent report proposed that mutant CALR interacts with the transcription factor Friend leukemia integration-1 (FLI1) and conveys it to the nucleus, where it regulates the MPL promoter.³⁸ However, this may be a consequence of enhanced JAK2 signaling rather than CALR translocating FLI1 to the nucleus, as FLI1 has been previously detected in the nucleus of megakaryocytes in JAK2-mutated ET patients.³⁹ In any case, topological analyses of subcellular localization are complicated by the low expression of mutant CALR protein, which is significantly less stable than its wild-type counterpart.^{22-24, 40}

Animal models

In addition to extensive work in cellular systems, several groups have also developed animal models to investigate the effects of mutant CALR. In zebrafish embryos, the injection of human type I but not type II mutant CALR mRNA resulted in an increase in CD41⁺ thrombocytes and a Mpl-dependent thrombocytosis that was abrogated using JAK1/JAK2 inhibitors.⁴¹ Most in vivo work to date has been performed in mouse models. In an early study using transplant of retroviral transduced bone marrow cells into lethally irradiated mice, type I and, to a lesser extent, type II mutant CALR produced thrombocytosis, with type I also showing eventual progression to myelofibrosis. This phenotype was MPL-dependent and accompanied by expansion of hematopoietic stem and progenitor cells (HSPCs) and the megakaryocytic lineage.⁴² A second retroviral model of the type I mutation showed similar results. In this case, a modest expansion of the Lin^-Sca1⁺cKit⁺ (LSK) compartment, which is enriched for HSPCs, was observed.²⁰ Similarly, transgenic expression of type I mutant CALR also produced an ET-like phenotype associated with increased numbers of HSPCs and megakaryocyte progenitors (MkPs), though HSPCs had no advantage in secondary competitive transplants.⁴³

Species-specific codon preferences mean that frameshift deletions or insertions in the mouse locus would generate a substantially different amino acid sequence to that seen in patients.⁴⁴ We therefore generated a mouse model in which DNA encoding the human novel C-terminal peptide associated with the type I mutation was knocked into the endogenous mouse Calr locus (ie, a humanized version of the CALR mutation). This approach yielded a hybrid protein with most of the mouse protein intact, but ending in the novel human sequence at the C-terminus, and ensuring an appropriate level of expression under the control of endogenous elements. This model also developed a strong ET-like phenotype, with a two- to three-fold increase in platelet levels, but did not progress to myelofibrosis. When bred to homozygosity, mice developed extreme thrombocytosis (platelet counts greater than 9 × 10⁶/μL) as well as splenomegaly, bone marrow fibrosis, and a further increase in the number of HSCs and MkPs. Interestingly, HSCs harboring mutant CALR had no advantage over their wild-type counterparts in transplantation experiments,⁴⁴ an observation reminiscent of results from JAK2 V617F knock-in mice.⁴⁵ Studies engineering frameshift deletions into the endogenous murine locus have typically shown a less prominent phenotype: use of a CRISPR-Cas9 approach to generate a 19-bp deletion in murine Calr yielded only a mild thrombocytosis and weak activation of JAK-STAT signaling.⁴⁶ Similarly, a recently published mouse model used a similar approach to engineer a 52- or 61-bp deletion in the endogenous mouse locus. The deletions led to increases in platelet levels of 35% and 15% respectively, with the 52-bp deletion also yielding a slow-rising advantage in transplantation experiments. The relatively mild phenotype could be attributed to weak activation of murine MPL by murine mutant CALR protein.⁴⁷

Together, animal studies have shown that expression of the human type I CALR mutant C-terminus in hematopoietic cells drives thrombocytosis and is associated with an expansion of the HSPC compartment, though transplantation experiments suggest these cells have no or only a slight competitive advantage.^{43, 44} All models show increased numbers of MKs within the bone marrow, and some models additionally show myelofibrosis at higher levels of mutant CALR expression, whether as a consequence of retroviral expression⁴² or homozygosity.⁴⁴ However, some questions remain unresolved. First, why do mouse models show no or minimal HSC advantage when human patients typically show a clonal disease? This may be due to varying genetic backgrounds and/or additional mutations in patients that are not present in mouse models. In addition, aging typically affects the microenvironment to which HSCs are exposed, which could explain the association of MPNs with increasing age in human patients. Finally, transplantation experiments represent a form of stress hematopoiesis in contrast to the steady state hematopoiesis occurring in patients. The recent use of neutral somatic mutations as barcodes has allowed the study of steady-state hematopoiesis in humans for the first time⁴⁸ and will additionally permit exploration of stem cell behavior and clonal dynamics in MPN patients. Another outstanding issue is the inability of type II CALR mutations to render a phenotype in animal models. While both type I and II CALR mutations are associated with disease in humans, it is currently unknown why only type I CALR mutant is able to drive an overt myeloproliferative phenotype in both mouse and zebrafish modeling, with type II CALR mutant described to drive mild or no thrombocytosis. Type II mutants may be unable to bind non-human MPL or efficiently activate downstream signaling.

Clinical aspects

Clinical manifestations

Both initial studies identifying CALR mutations noted a distinct clinical picture linked with CALR lesions compared to other driver mutations: CALR mutations were associated with higher platelet counts, lower WBC count, lower incidence of thrombosis, and better survival compared with JAK2 V617F patients.^{1, 2} Two meta-analyses and distinct cohorts of patients later corroborated these findings.^{49, 50} Analysis of mutations in individual hematopoietic clones showed an early acquisition of the lesion, compatible with an initiating event.^{1, 2} In addition, CALR mutations were found in patient hematopoietic stem cells and multipotent progenitors.² Taken together, these results agree with previously discussed studies showing that CALR mutations serve as a true driver of transformation.

Clinical differences have also been noted between distinct types of CALR lesions, with type I mutations seen significantly more frequently in MF than in ET.^{1, 2, 4, 51-53} In addition, differences in clinical behavior have been reported between type I and type II CALR mutations both in ET, where type II CALR mutations were associated with a significantly higher platelet count,^{52, 54} and in MF, where type I patients displayed a higher percentage of circulating blasts and frequency of mutations in EZH2.³

Thrombosis is the main cause of morbidity and mortality in MPN patients, particularly in polycythemia vera (PV) and ET.^{55, 56} Thrombosis incidence in CALR patients was originally reported to be less than half of that reported in JAK2 V617F patients.¹ However, a multivariate analysis in a large cohort of 1053 ET patients showed that differences in thrombosis incidence are not associated with the mutation per se but related to the differences in age and history of previous thrombosis between CALR and JAK2 V617F-mutated patients.⁵⁷ This was further confirmed in a smaller cohort, where the impact of CALR mutations on the risk of thrombosis was restricted to the group of patients younger than sixty.⁵⁸ Differences in the risk of thrombosis between type I and II CALR mutations were suggested in one study⁴ but failed to reach statistical significance in a larger collaborative study with 1027 patients.⁵⁴ A comparison of different leukocyte and platelet activation markers linked with thrombosis in ET patients found no statistically significant differences between CALR mutated and non-mutated patients.⁵⁹

Myelofibrotic transformation was reported to be significantly higher among CALR-mutated ET patients than JAK2 V617F patients in one initial report.² Follow-up studies were inconsistent, some showing no increased risk of transformation,^{49, 50} but 1 large-scale study again found a higher risk of transformation to MF.⁶⁰ Interestingly, the increase in the incidence of MF transformation among CALR-mutated ET patients appears to be restricted to type I mutations while patients with type II mutations displayed no differences to JAK2 V617F patients.⁴ This is in agreement with a recent study on post-essential thrombocythemia myelofibrosis (PET-MF) showing a time to MF progression significantly longer in type II than in type I CALR and JAK2 V617F mutations.⁶¹ As a consequence, type I mutations were overrepresented in PET-MF while in ET the distribution of the two most common CALR lesions was balanced.⁶¹ Importantly, no transformation from CALR-mutated ET to PV has been reported in any of the published cohorts.^{2, 49, 50} This stands in stark contrast to ET associated with JAK2 mutations and may reflect the lack of interaction between mutant CALR and EPOR.

Leukemic transformation was shown to be significantly lower in patients with CALR-mutated ET compared to those with JAK2 V617F mutated ET using a competing risk approach, but the differences did not reach statistical significance after adjusting for age.⁴⁹ A recent retrospective study found that CALR-mutated ET had a lower incidence of leukemic transformation compared to JAK2 V617F mutation and that the leukemic risk was not significantly affected by myelofibrotic transformation in a multivariate analysis.⁶² No differences in leukemic transformation in patients with MF^{51, 63} or leukemia-free survival⁶⁴ have been found.

Overall survival (OS) was increased in CALR-mutated patients compared to JAK2 V617F-mutated patients after correction for disease phenotype and the patient cohort¹; this was confirmed in MF using models that also corrected for patient age.^{17, 49} Some reports have found a significantly longer survival in type I CALR-mutated MF compared to type II,^{3, 65} while others reported similar trends that did not reach statistical significance.^{4, 66} In ET patients, no difference in OS between type I-like and type II-like patients was reported.⁶⁷ A recently published meta-analysis and large collaborative study have confirmed that CALR type I but not type II mutations are associated with a superior overall survival.^{64, 68} CALR- and JAK2-mutated MPNs are broadly similar in their spectra of co-occurring mutations.⁶⁹ Interestingly, type I-like CALR mutations in MF are not only associated with longer survival but may also correct the detrimental effect of ASXL1 and SRSF2 mutations, typically linked to a poorer prognosis.^{64, 70}

Overall, CALR mutations tend to be associated with a more benign natural history compared to JAK2 V617F-mutated disease. Differences between type I and II CALR mutations are also seen (Table 1), but the biological basis for this difference remains unclear.

Table 1. Clinical Differences Between CALR and JAK2 V617F Mutations.

Diagnostic approaches

CALR mutations are almost exclusively confined to ET and MF patients, though they were also identified in rare cases of myelodysplastic syndromes (including refractory anemia with ring sideroblasts (RARS)) and myelodysplastic-myeloproliferative syndromes.^{1, 2} CALR point mutations have also been described in some cases of chronic neutrophilic leukemia.^{72, 73} Due to their role as oncogenic drivers, CALR mutations have recently been added to the list of mutations considered major diagnostic criteria for ET and MF in the World Health Organization classification of hematological malignancies.⁷⁴ The screening for these mutations is part of the current diagnostic work-up for suspected ET and MF, usually after obtaining a negative result for the JAK2 V617F mutation.^{75, 76} Increasing amounts of genetic data for patients have also allowed the classification of MPNs based on their underlying biological mechanisms, not solely clinical features, resulting in improved prognostic predictions.⁶⁰

As more than 50 distinct CALR mutations have been described in ET and PMF and all of them are insertions or deletions, 2 main molecular diagnostic strategies are currently used: Sanger sequencing and fragment analysis, with the latter the most practical approach in terms of sensitivity and efficiency.⁷⁷ Other alternative methods have been proposed, including high resolution melting curve analysis and real-time PCR, but these techniques have been validated for only the two most frequent mutations and offer only modest sensitivity improvements over fragment analysis.⁷⁸ Next generation sequencing (NGS) strategies are quite attractive since the detection of additional mutations in MPN has a proven prognostic value. However, accurate indel variant calling is still challenging and distinguishing them from technical errors remains difficult.^{79, 80}

Treatment

The treatment goals for ET and MF patients are the same irrespective of the driver mutation: controlling the symptoms and extending the lifespan of the patients by reducing their thrombohemorrhagic risk. In ET, young patients without thrombotic risk factors generally benefit from thromboprophylaxis with low dose aspirin, while the combination of low dose aspirin and hydroxycarbamide significantly reduces the incidence of thrombosis in patients older than 60 years or with a previous thrombosis.^{56, 81, 82} Other available cytoreductive agents such as anagrelide⁵⁶ or interferon alfa^{83, 84} are used as second line options in specific cases, including young or pregnant patients requiring cytoreduction.

MF presents with a progressive clinical picture, ranging from the absence of symptoms to anemia, splenomegaly, constitutional symptoms, or transformation to acute myeloid leukemia. In contrast to ET, patients with MF tend to have a substantially reduced lifespan. However, the only curative treatment currently available for MF is allogeneic stem cell transplant. The current guidelines therefore recommend a symptom- and risk-based approach: although most patients are treated symptomatically, higher-risk and otherwise fit patients may be recommended for stem cell transplant. Management of symptoms include erythropoiesis-stimulating agents or danazol for anemia; hydroxycarbamide for splenomegaly, thrombocytosis, and leucocytosis; and ruxolitinb or fedratinib for splenomegaly and constitutional symptoms. Ruxolitinib and febratinib, both non-specific JAK inhibitors, exert their therapeutic effects through the downregulation of pro-inflammatory cytokines,^{85, 86} which is partially mediated via JAK1 inhibition.⁸⁷

Current recommendations for ET and MF are based on clinical trials conducted prior to the discovery of CALR or JAK2 V617F mutations.^{56, 75, 76, 81, 82, 88} Nevertheless, as explained above, CALR-mutated patients have some distinct clinical characteristics and could potentially benefit from a more tailored management. For instance, in a recently published retrospective study in low risk ET patients, low-dose aspirin was not only unable to reduce risk of thrombosis but was also associated with an increased risk of hemorrhage.⁷¹ However, most guidelines consider that this is not enough evidence to recommend withholding aspirin in CALR-mutated ET before these results are confirmed by clinical trials.^{75, 76} In addition to response to antiplatelet therapy, time free from cytoreduction is also shorter in CALR-mutated ET than in JAK2-mutated ET, usually because of extreme thrombocytosis in the former.⁷¹

Most patients diagnosed with CALR-mutated MPN have a satisfactory management with current antiplatelet and cytoreductive therapies, though some MF patients fail to respond to the currently available therapy. CALR mutation status does not significantly influence the outcome of treatment with ruxolitinib, as shown by retrospective analysis of CALR-mutated patients in the COMFORT-II trial.⁸⁹ In contrast, CALR mutations, particularly type I, are associated with a better overall survival and spleen response in patients treated with momelotinib, a JAK1/2 inhibitor.^{90, 91} Similarly, CALR mutations were found to be an independent factor for lower non-relapse mortality (NRM), improved progression free survival (PFS), and OS following allogenic bone marrow transplant in patients with MF, despite the large proportion of CALR-positive patients with intermediate-high and high risk scores at the time of transplantation.⁹² In another series of patients, those with CALR mutations were found to have a higher probability of clearing the minimal residual disease after transplant as compared to JAK2 V617F and MPL-mutated patients⁹³; this is regarded as a strong predictor of PFS.^{94, 95} This is in line with recent findings that type I-like CALR mutations independently predict a better outcome in allogeneic bone marrow transplants, leading to the inclusion of type I-like CALR mutations as an independent variable in MIPSS70, a prognostic system for transplantation in patients with MF.⁹⁶

There has also been interest in exploiting mutant CALR antigenicity as a target for cancer immunotherapy.^{97, 98} Cultured CD4⁺ T-cells from a patient with mutated CALR were able to recognize and kill autologous CD34⁺ HSCs, leading the authors to speculate that vaccinating patients with mutant CALR epitopes could induce the immune system to eliminate mutation-bearing HSCs.⁹⁸ A further analysis of mutant CALR associated neo-antigens identified a subset of potential interest for immunotherapy.⁹⁹

Future directions

In the 6 years since the first description of CALR mutations in ET and MF patients, significant insight has been gained into their biochemical and cell biological consequences and their clinical implications. It is clear that the primary mechanism of CALR-driven transformation lies in its interaction with MPL, which triggers JAK2-dependent signaling pathways, although it remains to be seen whether mutant CALR may also act through other pathways, such as Ca²⁺ signaling or transcriptional regulation.

Mouse models of CALR mutations consistently exhibit ET and MF-like phenotypes and can be used in the development of new targeted therapies. These models also raise new questions concerning the fundamental biology of CALR mutations. First, while both type I and type II mutations are associated with disease in humans and produce autonomous cell growth in several cell lines, only the former give rise to a consistent thrombocytosis phenotype in mice. Secondly, in contrast to ET and MF patients, CALR mutations do not confer a strong competitive advantage to HSCs. Further exploration of these intriguing observations will serve to illuminate the mechanisms by which CALR mutations cause disease.

Improved technologies and decreasing costs of sequencing have led to the generation of a wealth of genomic data on patients with MPNs. A knowledge bank approach has revealed a new genomic classification of the MPNs based on their underlying biological causes and has also allowed the development of personalized prognoses for individual patients.⁶⁰ Furthermore, single-cell approaches tracking somatic mutations are now being used in humans to examine clonal dynamics in healthy, steady-state hematopoiesis. Extension of these techniques to hematopoiesis in MPN, particularly at multiple time points through disease progression and treatment, will further illuminate the mechanisms underlying these diseases.

References

1Klampfl T, Gisslinger H, Harutyunyan AS et al. Somatic Mutations of Calreticulin in Myeloproliferative Neoplasms. N Engl J Med. 2013; 369: 2379–2390.
10.1056/NEJMoa1311347
CAS PubMed Web of Science® Google Scholar
2Nangalia J, Massie CE, Baxter EJ et al. Somatic CALR Mutations in Myeloproliferative Neoplasms with Nonmutated JAK2. N Engl J Med. 2013; 369: 2391–2405.
10.1056/NEJMoa1312542
CAS PubMed Web of Science® Google Scholar
3Tefferi A, Lasho TL, Tischer A et al. The prognostic advantage of calreticulin mutations in myelofibrosis might be confined to type 1 or type 1-like CALR variants. Blood. 2014; 124: 2465–2466.
10.1182/blood-2014-07-588426
CAS PubMed Web of Science® Google Scholar
4Pietra D, Rumi E, Ferretti VV et al. Differential clinical effects of different mutation subtypes in CALR-mutant myeloproliferative neoplasms. Leukemia. 2016; 30: 431–438.
10.1038/leu.2015.277
CAS PubMed Web of Science® Google Scholar
5Shtivelman E, Lifshitz B, Gale RP et al. Fused transcript of abl and bcr genes in chronic myelogenous leukaemia. Nature. 1985; 315: 550–554.
10.1038/315550a0
CAS PubMed Web of Science® Google Scholar
6Maxson JE, Gotlib J, Pollyea DA et al. Oncogenic CSF3R mutations in chronic neutrophilic leukemia and atypical CML. N Engl J Med. 2013; 368: 1781–1790.
10.1056/NEJMoa1214514
CAS PubMed Web of Science® Google Scholar
7James C, Ugo V, Le Couédic J-PP et al. A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera. Nature. 2005; 434: 1144–1148.
10.1038/nature03546
CAS PubMed Web of Science® Google Scholar
8Kralovics R, Passamonti F, Buser AS et al. A gain-of-function mutation of JAK2 in myeloproliferative disorders. N Engl J Med. 2005; 352: 1779–1790.
10.1056/NEJMoa051113
CAS PubMed Web of Science® Google Scholar
9Levine RL, Wadleigh M, Cools J et al. Activating mutation in the tyrosine kinase JAK2 in polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis. Cancer Cell. 2005; 7: 387–397.
10.1016/j.ccr.2005.03.023
CAS PubMed Web of Science® Google Scholar
10Baxter EJ, Scott LM, Campbell PJ et al. Acquired mutation of the tyrosine kinase JAK2 in human myeloproliferative disorders. Lancet. 2005; 365: 1054–1061.
10.1016/S0140-6736(05)71142-9
CAS PubMed Web of Science® Google Scholar
11Pikman Y, Lee BH, Mercher T et al. MPLW515L is a novel somatic activating mutation in myelofibrosis with myeloid metaplasia. PLoS Med. 2006; 3: 1140–1151.
10.1371/journal.pmed.0030270
CAS Web of Science® Google Scholar
12Pardanani AD, Levine RL, Lasho T et al. MPL515 mutations in myeloproliferative and other myeloid disorders: A study of 1182 patients. Blood. 2006; 108: 3472–3476.
10.1182/blood-2006-04-018879
CAS PubMed Web of Science® Google Scholar
13Afshar N, Black BE, Paschal BM. Retrotranslocation of the chaperone calreticulin from the endoplasmic reticulum lumen to the cytosol. Mol Cell Biol. 2005; 25: 8844–8853.
10.1128/MCB.25.20.8844-8853.2005
CAS PubMed Web of Science® Google Scholar
14Smith MJ, Koch GL. Multiple zones in the sequence of calreticulin (CRP55, calregulin, HACBP), a major calcium binding ER/SR protein. EMBO J. 1989; 8: 3581–3586.
10.1002/j.1460-2075.1989.tb08530.x
CAS PubMed Web of Science® Google Scholar
15Nakamura K, Zuppini A, Arnaudeau S et al. Functional specialization of calreticulin domains. J Cell Biol. 2001; 154: 961–972.
10.1083/jcb.200102073
CAS PubMed Web of Science® Google Scholar
16Eder-Azanza L, Navarro D, Aranaz P, Novo FJ, Cross NCP, Vizmanos JL. Bioinformatic analyses of CALR mutations in myeloproliferative neoplasms support a role in signaling. Leukemia. 2014; 28: 2106–2109.
10.1038/leu.2014.190
CAS PubMed Web of Science® Google Scholar
17Tefferi A, Lasho TL, Finke CM et al. CALR vs JAK2 vs MPL-mutated or triple-negative myelofibrosis: Clinical, cytogenetic and molecular comparisons. Leukemia. 2014; 28: 1472–1477.
10.1038/leu.2014.3
CAS PubMed Web of Science® Google Scholar
18Lundberg P, Karow A, Nienhold R et al. Clonal evolution and clinical correlates of somatic mutations in myeloproliferative neoplasms. Blood. 2014; 123: 2220–2228.
10.1182/blood-2013-11-537167
CAS PubMed Web of Science® Google Scholar
19McGaffin G, Harper K, Stirling D, McLintock L. JAK2 V617F and CALR mutations are not mutually exclusive; findings from retrospective analysis of a small patient cohort. Br J Haematol. 2014; 167: 276–278.
10.1111/bjh.12969
CAS PubMed Web of Science® Google Scholar
20Elf S, Abdelfattah NS, Chen E et al. Mutant calreticulin requires both its mutant C-terminus and the thrombopoietin receptor for oncogenic transformation. Cancer Discov. 2016; 6: 368–381.
10.1158/2159-8290.CD-15-1434
CAS PubMed Web of Science® Google Scholar
21Nivarthi H, Chen D, Cleary C et al. Thrombopoietin receptor is required for the oncogenic function of CALR mutants. Leukemia. 2016; 30: 1759–1763.
10.1038/leu.2016.32
CAS PubMed Web of Science® Google Scholar
22Kollmann K, Warsch W, Gonzalez-Arias C et al. A novel signalling screen demonstrates that CALR mutations activate essential MAPK signalling and facilitate megakaryocyte differentiation. Leukemia. 2017; 31: 934–944.
10.1038/leu.2016.280
CAS PubMed Web of Science® Google Scholar
23Araki M, Yang Y, Masubuchi N et al. Activation of the thrombopoietin receptor by mutant calreticulin in CALR-mutant myeloproliferative neoplasms. Blood. 2016; 127: 1307–1316.
10.1182/blood-2015-09-671172
CAS PubMed Web of Science® Google Scholar
24Chachoua I, Pecquet C, El-Khoury M et al. Thrombopoietin receptor activation by myeloproliferative neoplasm associated calreticulin mutants. Blood. 2016; 127: 1325–1335.
10.1182/blood-2015-11-681932
CAS PubMed Web of Science® Google Scholar
25Elf S, Abdelfattah NS, Baral AJ et al. Defining the requirements for the pathogenic interaction between mutant calreticulin and MPL in MPN. Blood. 2018; 131: 782–786.
10.1182/blood-2017-08-800896
CAS PubMed Web of Science® Google Scholar
26Araki M, Yang Y, Imai M et al. Homomultimerization of mutant calreticulin is a prerequisite for MPL binding and activation. Leukemia. 2019; 33: 122–131.
10.1038/s41375-018-0181-2
CAS PubMed Web of Science® Google Scholar
27Carpio MA, Decca MB, Lopez Sambrooks C et al. Calreticulin-dimerization induced by post-translational arginylation is critical for stress granules scaffolding. Int J Biochem Cell Biol. 2013; 45: 1223–1235.
10.1016/j.biocel.2013.03.017
CAS PubMed Web of Science® Google Scholar
28Pecquet C, Chachoua I, Roy A et al. Calreticulin mutants as oncogenic rogue chaperones for TpoR and traffic-defective pathogenic TpoR mutants. Blood. 2019; 133: 2669–2681.
10.1182/blood-2018-09-874578
CAS PubMed Web of Science® Google Scholar
29Balligand T, Achouri Y, Pecquet C et al. Pathologic activation of thrombopoietin receptor and JAK2-STAT5 pathway by frameshift mutants of mouse calreticulin. Leukemia. 2016; 30: 1775–1778.
10.1038/leu.2016.47
CAS PubMed Web of Science® Google Scholar
30Takei H, Edahiro Y, Mano S et al. Skewed megakaryopoiesis in human induced pluripotent stem cell-derived haematopoietic progenitor cells harbouring calreticulin mutations. Br J Haematol. 2018; 181: 791–802.
10.1111/bjh.15266
CAS PubMed Web of Science® Google Scholar
31Rampal R, Al-shahrour F, Abdel-wahab O et al. Integrated genomic analysis illustrates the central role of JAK-STAT pathway activation in myeloproliferative neoplasm pathogenesis. Blood. 2015; 123: 123–134.
10.1182/blood-2014-02-554634
Web of Science® Google Scholar
32Lau WWY, Hannah R, Green AR et al. The JAK-STAT signaling pathway is differentially activated in CALR-positive compared with JAK2V617F-positive ET patients. Blood. 2015; 125: 1679–1681.
10.1182/blood-2014-12-618074
CAS PubMed Web of Science® Google Scholar
33Di Buduo CA, Abbonante V, Marty C et al. Defective interaction of mutant calreticulin and SOCE in megakaryocytes from patients with myeloproliferative neoplasms. Blood. 2019;doi: https://doi.org/10.1182/blood.2019001103.
10.1182/blood.2019001103
Google Scholar
34Di Buduo CA, Moccia F, Battiston M et al. The importance of calcium in the regulation of megakaryocyte function. Haematologica. 2014; 99: 769–778.
10.3324/haematol.2013.096859
CAS PubMed Web of Science® Google Scholar
35N⊘rgaard Toft K, Larsen N, J⊘rgensen FS et al. Small angle X-ray scattering study of calreticulin reveals conformational plasticity. Biochim Biophys Acta - Proteins Proteomics. 2008; 1784: 1265–1270.
10.1016/j.bbapap.2008.05.005
Web of Science® Google Scholar
36Chouquet A, Païdassi H, Ling WL et al. X-ray structure of the human calreticulin globular domain reveals a peptide-binding area and suggests a multi-molecular mechanism. PLoS One. 2011; 6: e17886.
10.1371/journal.pone.0017886
CAS PubMed Web of Science® Google Scholar
37Shivarov V, Ivanova M, Tiu RV. Mutated calreticulin retains structurally disordered C terminus that cannot bind Ca2+: Some mechanistic and therapeutic implications. Blood Cancer J. 2014; 4: e185.
10.1038/bcj.2014.7
CAS PubMed Web of Science® Google Scholar
38Pronier E, Cifani P, Merlinsky TR et al. Targeting the CALR interactome in myeloproliferative neoplasms. JCI insight. 2018; 3: e122703.
10.1172/jci.insight.122703
PubMed Web of Science® Google Scholar
39Bock O, Hussein K, Neusch M et al. Transcription factor Fli-1 expression by bone marrow cells in chronic myeloproliferative disorders is independent of an underlying JAK2 (V617F) mutation. Eur J Haematol. 2006; 77: 463–470.
10.1111/j.0902-4441.2006.t01-1-EJH2826.x
CAS PubMed Web of Science® Google Scholar
40Han L, Schubert C, Köhler J et al. Calreticulin-mutant proteins induce megakaryocytic signaling to transform hematopoietic cells and undergo accelerated degradation and Golgi-mediated secretion. J Hematol Oncol. 2016; 9: 1–14.
10.1186/s13045-016-0275-0
CAS PubMed Web of Science® Google Scholar
41Lim KH, Chang YC, Chiang YH et al. Expression of CALR mutants causes mpl-dependent thrombocytosis in zebrafish. Blood Cancer J. 2016; 6: e481.
10.1038/bcj.2016.83
PubMed Web of Science® Google Scholar
42Marty C, Pecquet C, Nivarthi H et al. Calreticulin mutants in mice induce an MPL-dependent thrombocytosis with frequent progression to myelofibrosis. Blood. 2016; 127: 1317–1324.
10.1182/blood-2015-11-679571
CAS PubMed Web of Science® Google Scholar
43Shide K, Kameda T, Yamaji T et al. Calreticulin mutant mice develop essential thrombocythemia that is ameliorated by the JAK inhibitor ruxolitinib. Leukemia. 2017; 31: 1136–1144.
10.1038/leu.2016.308
CAS PubMed Web of Science® Google Scholar
44Li J, Prins D, Park HJ et al. Mutant calreticulin knockin mice develop thrombocytosis andmyelofibrosis without a stemcell self-renewal advantage. Blood. 2018; 131: 649–661.
10.1182/blood-2017-09-806356
CAS PubMed Web of Science® Google Scholar
45Li J, Kent DG, Chen E, Green AR. Mouse models of myeloproliferative neoplasms: JAK of all grades. DMM Dis Model Mech. 2011; 4: 311–317.
10.1242/dmm.006817
CAS PubMed Web of Science® Google Scholar
46Shide K, Kameda T, Kamiunten A et al. Mice with Calr mutations homologous to human CALR mutations only exhibit mild thrombocytosis. Blood Cancer J. 2019; 9: 42.
10.1038/s41408-019-0202-z
PubMed Web of Science® Google Scholar
47Balligand T, Achouri Y, Pecquet C et al. Knock-in of murine Calr del52 induces essential thrombocythemia with slow-rising dominance in mice and reveals key role of Calr exon 9 in cardiac development. Leukemia. 2019;doi:10.1038/s41375-019-0538-1.
Google Scholar
48Lee-Six H. Øbro NF, Shepherd MS, et al. Population dynamics of normal human blood inferred from somatic mutations. Nature. 2018; 561: 473–478.
10.1038/s41586-018-0497-0
CAS PubMed Web of Science® Google Scholar
49Rumi E, Pietra D, Ferretti V et al. JAK2 or CALR mutation status defines subtypes of essential thrombocythemia with substantially different clinical course and outcomes. Blood. 2014; 123: 1544–1551.
10.1182/blood-2013-11-539098
CAS PubMed Web of Science® Google Scholar
50Rotunno G, Mannarelli C, Guglielmelli P et al. Impact of calreticulin mutations on clinical and hematological phenotype and outcome in essential thrombocythemia. Blood. 2014; 123: 1552–1555.
10.1182/blood-2013-11-538983
CAS PubMed Web of Science® Google Scholar
51Rumi E, Pietra D, Pascutto C et al. Clinical effect of driver mutations of JAK2, CALR, or MPL in primary myelofibrosis. Blood. 2014; 124: 1062–1069.
10.1182/blood-2014-05-578435
CAS PubMed Web of Science® Google Scholar
52Cabagnols X, Defour JP, Ugo V et al. Differential association of calreticulin type 1 and type 2 mutations with myelofibrosis and essential thrombocytemia: Relevance for disease evolution. Leukemia. 2015; 29: 249–252.
10.1038/leu.2014.270
CAS PubMed Web of Science® Google Scholar
53Passamonti F, Mora B, Giorgino T et al. Driver mutations’ effect in secondary myelofibrosis: An international multicenter study based on 781 patients. Leukemia. 2017; 31: 970–973.
10.1038/leu.2016.351
CAS PubMed Web of Science® Google Scholar
54Tefferi A, Wassie EA, Guglielmelli P et al. Type 1 versus Type 2 calreticulin mutations in essential thrombocythemia: A collaborative study of 1027 patients. Am J Hematol. 2014; 89: E121–E124.
10.1002/ajh.23743
CAS PubMed Web of Science® Google Scholar
55Marchioli R, Finazzi G, Landolfi R et al. Vascular and neoplastic risk in a large cohort of patients with polycythemia vera. J Clin Oncol. 2005; 23: 2224–2232.
10.1200/JCO.2005.07.062
PubMed Web of Science® Google Scholar
56Harrison CN, Campbell PJ, Buck G et al. Hydroxyurea Compared with Anagrelide in High-Risk Essential Thrombocythemia. N Engl J Med. 2005; 353: 33–45.
10.1056/NEJMoa043800
CAS PubMed Web of Science® Google Scholar
57Finazzi G, Carobbio A, Guglielmelli P et al. Calreticulin mutation does not modify the IPSET score for predicting the risk of thrombosis among 1150 patients with essential thrombocythemia. Blood. 2014; 124: 2611–2612.
10.1182/blood-2014-08-596676
CAS PubMed Web of Science® Google Scholar
58Gangat N, Wassie EA, Lasho TL et al. Mutations and thrombosis in essential thrombocythemia: Prognostic interaction with age and thrombosis history. Eur J Haematol. 2015; 94: 31–36.
10.1111/ejh.12389
CAS PubMed Web of Science® Google Scholar
59Torregrosa JM, Ferrer-Marín F, Lozano ML et al. Impaired leucocyte activation is underlining the lower thrombotic risk of essential thrombocythaemia patients with CALR mutations as compared with those with the JAK2 mutation. Br J Haematol. 2016; 172: 813–815.
10.1111/bjh.13539
CAS PubMed Web of Science® Google Scholar
60Grinfeld J, Nangalia J, Baxter EJ et al. Classification and Personalized Prognosis in Myeloproliferative Neoplasms. N Engl J Med. 2018; 379: 1416–1430.
10.1056/NEJMoa1716614
CAS PubMed Web of Science® Google Scholar
61Rotunno G, Pacilli A, Artusi V et al. Epidemiology and clinical relevance of mutations in postpolycythemia vera and postessential thrombocythemia myelofibrosis: A study on 359 patients of the AGIMM group. Am J Hematol. 2016; 91: 681–686.
10.1002/ajh.24377
CAS PubMed Web of Science® Google Scholar
62Alvarez-Larrán A, Senín A, Fernández-Rodríguez C et al. Impact of genotype on leukaemic transformation in polycythaemia vera and essential thrombocythaemia. Br J Haematol. 2017; 178: 764–771.
10.1111/bjh.14762
CAS PubMed Web of Science® Google Scholar
63Guglielmelli P, Rotunno G, Fanelli T et al. Validation of the differential prognostic impact of type 1/type 1-like versus type 2/type 2-like CALR mutations in myelofibrosis. Blood Cancer J. 2015; 5: e360.
10.1038/bcj.2015.90
CAS PubMed Web of Science® Google Scholar
64Tefferi A, Nicolosi M, Mudireddy M et al. Driver mutations and prognosis in primary myelofibrosis: Mayo-Careggi MPN alliance study of 1,095 patients. Am J Hematol. 2018; 93: 348–355.
10.1002/ajh.24978
CAS PubMed Web of Science® Google Scholar
65Godfrey AL, Chen E, Massie CE et al. STAT1 activation in association with JAK2 exon 12 mutations. Haematologica. 2015; 101: e15–e19.
10.3324/haematol.2015.128546
PubMed Web of Science® Google Scholar
66Li B, Xu J, Wang J et al. Calreticulin mutations in Chinese with primary myelofibrosis. Haematologica. 2014; 99: 1697–1700.
10.3324/haematol.2014.109249
CAS PubMed Web of Science® Google Scholar
67Elala YC, Lasho TL, Gangat N et al. Calreticulin variant stratified driver mutational status and prognosis in essential thrombocythemia. Am J Hematol. 2016; 91: 503–506.
10.1002/ajh.24338
CAS PubMed Web of Science® Google Scholar
68Kourie HR, Ameye L, Paesmans M, Bron D. Improved survival in patients with CALR1 compared to CALR2 mutated primary myelofibrosis: a meta-analysis. Br J Haematol. 2017; 179: 846–848.
10.1111/bjh.14259
PubMed Web of Science® Google Scholar
69Agarwal R, Blombery P, McBean M et al. Clinicopathological differences exist between CALR- and JAK2-mutated myeloproliferative neoplasms despite a similar molecular landscape: data from targeted next-generation sequencing in the diagnostic laboratory. Ann Hematol. 2017; 96: 725–732.
10.1007/s00277-017-2937-6
CAS PubMed Web of Science® Google Scholar
70Tefferi A, Guglielmelli P, Lasho TL et al. CALR and ASXL1 mutations-based molecular prognostication in primary myelofibrosis: An international study of 570 patients. Leukemia. 2014; 28: 1494–1500.
10.1038/leu.2014.57
CAS PubMed Web of Science® Google Scholar
71Lasho TL, Elliott MA, Pardanani A, Tefferi A. CALR mutation studies in chronic neutrophilic leukemia. Am J Hematol. 2014; 89: 450.
10.1002/ajh.23665
CAS PubMed Web of Science® Google Scholar
72Elliott MA, Pardanani A, Hanson CA et al. ASXL1 mutations are frequent and prognostically detrimental in CSF3R-mutated chronic neutrophilic leukemia. Am J Hematol. 2015; 90: 653–656.
10.1002/ajh.24031
CAS PubMed Web of Science® Google Scholar
73Arber DA, Orazi A, Hasserjian R et al. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood. 2016; 127: 2391–2405.
10.1182/blood-2016-03-643544
CAS PubMed Web of Science® Google Scholar
74Mesa RA, Jamieson C, Bhatia R et al. NCCN Guidelines Insights: Myeloproliferative Neoplasms, Version 2.2018. J Natl Compr Canc Netw. 2017; 15: 1193–1207.
10.6004/jnccn.2017.0157
PubMed Web of Science® Google Scholar
75Barbui T, Tefferi A, Vannucchi AM et al. Philadelphia chromosome-negative classical myeloproliferative neoplasms: Revised management recommendations from European LeukemiaNet. Leukemia. 2018; 32: 1057–1069.
10.1038/s41375-018-0077-1
PubMed Web of Science® Google Scholar
76Xia D, Hasserjian RP. Molecular testing for JAK2, MPL, and CALR in myeloproliferative neoplasms. Am J Hematol. 2016; 91: 1277–1280.
10.1002/ajh.24578
CAS PubMed Web of Science® Google Scholar
77Chi J, Manoloukos M, Pierides C et al. Calreticulin mutations in myeloproliferative neoplasms and new methodology for their detection and monitoring. Ann Hematol. 2014; 94: 399–408.
10.1007/s00277-014-2232-8
PubMed Web of Science® Google Scholar
78Kluk MJ, Lindsley RC, Aster JC et al. Validation and Implementation of a Custom Next-Generation Sequencing Clinical Assay for Hematologic Malignancies. J Mol Diagnostics. 2016; 18: 507–515.
10.1016/j.jmoldx.2016.02.003
CAS PubMed Web of Science® Google Scholar
79Kim B-Y, Park JH, Jo H-Y et al. Optimized detection of insertions/deletions (INDELs) in whole-exome sequencing data. Bandapalli OR, ed. PLoS One. 2017; 12: e0182272.
10.1371/journal.pone.0182272
PubMed Web of Science® Google Scholar
80Cortelazzo S, Finazzi G, Ruggeri M et al. Hydroxyurea for patients with essential thrombocythemia and a high risk of thrombosis. N Engl J Med. 1995; 332: 1132–1137.
10.1056/NEJM199504273321704
CAS PubMed Web of Science® Google Scholar
81Alvarez-Larrán A, Pereira A, Arellano-Rodrigo E et al. Cytoreduction plus low-dose aspirin versus cytoreduction alone as primary prophylaxis of thrombosis in patients with high-risk essential thrombocythaemia: An observational study. Br J Haematol. 2013; 161: 865–871.
10.1111/bjh.12321
CAS PubMed Web of Science® Google Scholar
82Gilbert HS. Long term treatment of myeloproliferative disease with interferon-α- 2b: Feasibility and efficacy. Cancer. 1998; 83: 1205–1213.
10.1002/(SICI)1097-0142(19980915)83:6<1205::AID-CNCR21>3.0.CO;2-8
CAS PubMed Web of Science® Google Scholar
83Saba R, Jabbour E, Giles F et al. Interferon α therapy for patients with essential thrombocythemia: Final results of a Phase II study initiated in 1986. Cancer. 2005; 103: 2551–2557.
10.1002/cncr.21086
CAS PubMed Web of Science® Google Scholar
84Verstovsek S, Kantarjian H, Mesa RA et al. Safety and efficacy of INCB018424, a JAK1 and JAK2 inhibitor, in myelofibrosis. N Engl J Med. 2010; 363: 1117–1127.
10.1056/NEJMoa1002028
CAS PubMed Web of Science® Google Scholar
85Pardanani A, Tefferi A, Jamieson C et al. A phase 2 randomized dose-ranging study of the JAK2-selective inhibitor fedratinib (SAR302503) in patients with myelofibrosis. Blood Cancer J. 2015; 5: e335.
10.1038/bcj.2015.63
CAS PubMed Web of Science® Google Scholar
86Quintás-Cardama A, Vaddi K, Liu P et al. Preclinical characterization of the selective JAK1/2 inhibitor INCB018424: Therapeutic implications for the treatment of myeloproliferative neoplasms. Blood. 2010; 115: 3109–3117.
10.1182/blood-2009-04-214957
CAS PubMed Web of Science® Google Scholar
87Harrison C, Kiladjian JJ, Al-Ali HK et al. JAK inhibition with ruxolitinib versus best available therapy for myelofibrosis. N Engl J Med. 2012; 366: 787–798.
10.1056/NEJMoa1110556
CAS PubMed Web of Science® Google Scholar
88Alvarez-Larrán A, Pereira A, Guglielmelli P et al. Antiplatelet therapy versus observation in low-risk essential thrombocythemia with a CALR mutation. Haematologica. 2016; 101: 926–931.
10.3324/haematol.2016.146654
CAS PubMed Web of Science® Google Scholar
89Guglielmelli P, Rotunno G, Bogani C et al. Ruxolitinib is an effective treatment for CALR-positive patients with myelofibrosis. Br J Haematol. 2016; 173: 938–940.
10.1111/bjh.13644
CAS PubMed Web of Science® Google Scholar
90Pardanani A, Abdelrahman RA, Finke C et al. Genetic determinants of response and survival in momelotinib-treated patients with myelofibrosis. Leukemia. 2015; 29: 741–744.
10.1038/leu.2014.306
CAS PubMed Web of Science® Google Scholar
91Tefferi A, Barraco D, Lasho TL et al. Momelotinib therapy for myelofibrosis: A 7-year follow-up. Blood Cancer J. 2018; 8: 29.
10.1038/s41408-018-0067-6
PubMed Web of Science® Google Scholar
92Kröger N, Panagiota V, Badbaran A et al. Impact of Molecular Genetics on Outcome in Myelofibrosis Patients after Allogeneic Stem Cell Transplantation. Biol Blood Marrow Transplant. 2017; 23: 1095–1101.
10.1016/j.bbmt.2017.03.034
PubMed Web of Science® Google Scholar
93Wolschke C, Badbaran A, Zabelina T et al. Impact of molecular residual disease post allografting in myelofibrosis patients. Bone Marrow Transplant. 2017; 52: 1526–1529.
10.1038/bmt.2017.157
CAS PubMed Web of Science® Google Scholar
94Alchalby H, Badbaran A, Zabelina T et al. Impact of JAK2V617F mutation status, allele burden, and clearance after allogeneic stem cell transplantation for myelofibrosis. Blood. 2010; 116: 3572–3581.
10.1182/blood-2009-12-260588
CAS PubMed Web of Science® Google Scholar
95Buckley SA, Appelbaum FR, Walter RB. Prognostic and therapeutic implications of minimal residual disease at the time of transplantation in acute leukemia. Bone Marrow Transplant. 2013; 48: 630–641.
10.1038/bmt.2012.139
CAS PubMed Web of Science® Google Scholar
96Guglielmelli P, Lasho TL, Rotunno G et al. MIPSS70: Mutation-enhanced international prognostic score system for transplantation-age patients with primary myelofibrosis. J Clin Oncol. 2018; 36: 310–318.
10.1200/JCO.2017.76.4886
CAS PubMed Web of Science® Google Scholar
97Holmström MO, Riley CH, Svane IM et al. exon 9 mutations are shared neoantigens in patients with CALR mutant chronic myeloproliferative neoplasms. Leukemia. 2016; 30: 2413–2416.
10.1038/leu.2016.233
CAS PubMed Web of Science® Google Scholar
98Holmström MO, Martinenaite E, Ahmad SM et al. The calreticulin (CALR) exon 9 mutations are promising targets for cancer immune therapy. Leukemia. 2018; 32: 429–437.
10.1038/leu.2017.214
CAS PubMed Web of Science® Google Scholar
99Schischlik F, Jäger R, Rosebrock F et al. Mutational landscape of the transcriptome offers putative targets for immunotherapy of myeloproliferative neoplasms. Blood. 2019; 134: 199–210.
10.1182/blood.2019000519
CAS PubMed Web of Science® Google Scholar

Citing Literature

Volume4, Issue1

February 2020

e333

This article also appears in:

Reviews

Mutant Calreticulin in the Myeloproliferative Neoplasms

Abstract

Introduction