Clinical and molecular response to interferon-α therapy in essential thrombocythemia patients with CALR mutations

Mutations in MPNs: prognostic implications, window to biology, and impact on treatment decisions

The last decade has witnessed tremendous scientific advances, ushered in by the JAK2 V617F discovery, contributing to enhanced diagnostic capability and understanding of the biology of myeloproliferative neoplasms (MPNs). Discovery of the calreticulin mutations filled a diagnostic gap; more recent work sheds light on its contribution to disease pathogenesis, and prognosis. Recent studies have also identified novel JAK2 and MPL mutations in patients with essential thrombocythemia and myelofibrosis (MF). Especially in MF, the driver mutational profile has prognostic implications, with additive contributions from the acquisition of additional somatic mutations. The hope is that sophisticated molecular profiling will not only aid in prognostication, but also guide selection of therapy for patients with MPNs.

Mutations in MPNs: prognostic implications, window to biology, and impact on treatment decisions

The last decade has witnessed tremendous scientific advances, ushered in by the JAK2 V617F discovery, contributing to enhanced diagnostic capability and understanding of the biology of myeloproliferative neoplasms (MPNs). Discovery of the calreticulin mutations filled a diagnostic gap; more recent work sheds light on its contribution to disease pathogenesis, and prognosis. Recent studies have also identified novel JAK2 and MPL mutations in patients with essential thrombocythemia and myelofibrosis (MF). Especially in MF, the driver mutational profile has prognostic implications, with additive contributions from the acquisition of additional somatic mutations. The hope is that sophisticated molecular profiling will not only aid in prognostication, but also guide selection of therapy for patients with MPNs.

How I treat essential thrombocythemia

Essential thrombocythemia (ET) is an indolent myeloproliferative neoplasm that may be complicated by vascular events, including both thrombosis and bleeding. This disorder may also transform into more aggressive myeloid neoplasms, in particular into myelofibrosis. The identification of somatic mutations of JAK2, CALR, or MPL, found in about 90% of patients, has considerably improved the diagnostic approach to this disorder. Genomic profiling also holds the potential to improve prognostication and, more generally, clinical decision-making because the different driver mutations are associated with distinct clinical features. Prevention of vascular events has been so far the main objective of therapy, and continues to be extremely important in the management of patients with ET. Low-dose aspirin and cytoreductive drugs can be administered to this purpose, with cytoreductive treatment being primarily given to patients at high risk of vascular complications. Currently used cytoreductive drugs include hydroxyurea, mainly used in older patients, and interferon α, primarily given to younger patients. There is a need for disease-modifying drugs that can eradicate clonal hematopoiesis and/or prevent progression to more aggressive myeloid neoplasms, especially in younger patients. In this article, we use a case-based discussion format to illustrate our approach to diagnosis and treatment of ET.

Monitoring Minimal Residual Disease in the Myeloproliferative Neoplasms: Current Applications and Emerging Approaches

The presence of acquired mutations within the JAK2, CALR, and MPL genes in the majority of patients with myeloproliferative neoplasms (MPN) affords the opportunity to utilise these mutations as markers of minimal residual disease (MRD). Reduction of the mutated allele burden has been reported in response to a number of therapeutic modalities including interferon, JAK inhibitors, and allogeneic stem cell transplantation; novel therapies in development will also require assessment of efficacy. Real-time quantitative PCR has been widely adopted for recurrent point mutations with assays demonstrating the specificity, sensitivity, and reproducibility required for clinical utility. More recently, approaches such as digital PCR have demonstrated comparable, if not improved, assay characteristics and are likely to play an increasing role in MRD monitoring. While next-generation sequencing is increasingly valuable as a tool for diagnosis of MPN, its role in the assessment of MRD requires further evaluation.

Differential Dynamics of CALR Mutant Allele Burden in Myeloproliferative Neoplasms during Interferon Alfa Treatment

Discovery of somatic mutations in the calreticulin gene (CALR) has identified a subgroup of Philadelphia-negative chronic myeloproliferative neoplasms (MPN) with separate haematological characteristics and prognosis. CALR mutations serve as novel markers both of diagnostic value and as targets for monitoring molecular responses during therapy. Interferon-α (IFN) selectively targets the malignant clone in a subset of MPN patients and can induce both haematological and molecular remissions in CALR mutated essential thrombocythemia (ET) patients. We investigated the response to IFN in a cohort of 21 CALR mutated MPN patients including ET, prefibrotic primary myelofibrosis (pre-PMF), and primary myelofibrosis (PMF) with a median follow-up of 31 months. For evaluation of a molecular response, we developed highly sensitive quantitative PCR (qPCR) assays for monitoring the mutant allele burden of the two most prevalent CALR mutations (type 1 and type 2). Thirteen patients (62%) experienced a decrease in the mutant allele burden with a median decline of 29% from baseline. However, only four patients, including patients with ET, pre-PMF, and PMF diagnosis, achieved molecular responder (MR) status with >50% reduction in mutant allele burden according to European LeukemiaNet (ELN) guidelines. MR patients displayed significant differences in the dynamics of the CALR mutant load with regard to time to response and dynamics in mutant allele burden after discontinuation of IFN treatment. Furthermore, we highlight the prognostic value of the CALR mutant allele burden by showing a close association with leucocyte- and platelet counts, hemoglobin concentration, in addition to plasma lactate dehydrogenase (LDH) irrespective of molecular response and treatment status.

Second malignancies in hydroxyurea and interferon-treated Philadelphia-negative myeloproliferative neoplasms

OBJECTIVE

In an era of controversy in regard to 'hydroxyurea-leukaemogenicity' and when interferon-alfa2 (IFN) is being revived in the treatment of Philadelphia-negative myeloproliferative neoplasms (MPNs), we aim in this single-centre observational study to describe the frequencies of second malignancies in a cohort of MPN patients treated with hydroxyurea (HU) or IFN monotherapy or the combination of these agents.

PATIENTS AND METHODS

Records of a MPN cohort of 196 patients were reviewed, and a retrospective analysis was performed on 90 patients treated with HU, 38 patients treated with IFN and 68 patients treated with both IFN and HU. Logistic regression was used to compare frequencies in second malignancies.

RESULTS

Patients treated with HU had a significantly higher risk of developing all second malignancies compared with patients treated with IFN [HU vs. IFN: OR of 4.01 (95%CI: 1.12-14.27, P-value: 0.023) and HU-IFN vs. IFN: OR 5.58 (95%CI: 1.55-20.15, P-value: 0.004)].

CONCLUSION

We have found an increased risk of second malignancies in MPN patients treated with HU compared with patients treated with IFN.

How to Treat Essential Thrombocythemia and Polycythemia Vera

Polycythemia vera and essential thrombocythemia (ET) are chronic myeloproliferative neoplasms associated with thrombotic or hemorrhagic complications, and increased risk of transformation to myelofibrosis and acute myeloid leukemia. The main goal of therapy is aimed at preventing vascular events that are the leading cause of morbidity and mortality in these patients. Accordingly, risk stratification is the basis for deciding when to treat a patient with cytoreductive therapy. The European LeukemiaNet has developed a series of management recommendations for front-line and second-line therapy to provide the optimal treatment for the individual patient. There is still controversy about the efficacy and safety of several modalities of cytoreductive treatment in the long-term for both diseases and in the use of antiplatelet therapy in ET. The presence of JAK2V617F and CALR mutations in patients with ET has been related to different thrombotic risks, and this will probably lead to different therapeutic approaches in the near future. On the other hand, the near normal life expectancy of these patients makes a careful analysis of the benefits and risks associated with treatment essential. This review provides our current management strategy of patients with polycythemia vera and ET.

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BIOLOGICAL ASPECTS OF JAK/STAT SIGNALING IN BCR-ABL-NEGATIVE MYELOPROLIFERATIVE NEOPLASMS: Myeloproliferative disorders more recently named Myeloproliferative neoplasms (MPN) display several clinical entities: chronic myeloid leukemia (CML), the classical MPN including polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF) and atypical and unclassifiable NMP. The term MPN is mostly used for classical BCR-ABL-negative (myeloproliferative disorder) (ET, PV, PMF). These are clonal diseases resulting from the transformation of an hematopoietic stem cell and leading to an abnormal production of myeloid cells. The genetic defects responsible for the myeloproliferative abnormalities are called « driver » mutations and all result in deregulation of the cytokine receptor / JAK2 / STAT axis. Among them, JAK2, the thrombopoietin receptor (MPL) and calreticulin (CALR) mutations are found in around 90% of the cases. These driver MPN mutations can be associated with other driver mutations also found in other hematological malignancies, especially in PMFs. These are chronic diseases with major risks being thrombosis, hemorrhage and cytopenias for PMF and the long-term progression to myelofibrosis and the transformation to leukemia. Most recent therapeutic have focused on targeting the JAK2 signaling pathway directly by inhibitors of JAK2 or indirectly. Interferon a allows in some cases hematologic and molecular remission patients.

Mutant calreticulin: when a chaperone becomes intrusive

In this issue of Blood, Marty et al, Chachoua et al, and Araki et al report results of studies unraveling the molecular pathogenesis of CALR-mutant myeloproliferative neoplasms (MPNs). Together, these 3 reports define a novel disease paradigm, whereby a mutant chaperone constitutively activates receptor signaling through an abnormal interaction with the thrombopoietin (TPO) receptor (MPL).

CALR mutation profile in Irish patients with myeloproliferative neoplasms

Insertion and/or deletion mutations of the CALR gene have recently been demonstrated to be the second most common driver mutations in the myeloproliferative neoplasms (MPNs) of essential thrombocythemia (ET) and primary myelofibrosis (PMF). Given the diagnostic and emerging prognostic significance of these mutations, in addition to the geographical heterogeneity reported, the incidence of CALR mutations was determined in an Irish cohort of patients with MPNs with a view to incorporate this analysis into a prospective screening program. A series of 202 patients with known or suspected ET and PMF were screened for the presence of CALR mutations. CALR mutations were detected in 58 patients. Type 1 and Type 1-like deletion mutations were the most common (n=40) followed by Type 2 and Type 2-like insertion mutations (n=17). The CALR mutation profile in Irish ET and PMF patients appears similar to that in other European populations. Establishment of this mutational profile allows the introduction of a rational, molecular diagnostic algorithm in cases of suspected ET and PMF that will improve clinical management.

Evolving Therapeutic Strategies for the Classic Philadelphia-Negative Myeloproliferative Neoplasms

Despite the emergence of JAK inhibitors, there is a need for disease-modifying treatments for Philadelphia-negative myeloproliferative neoplasms (MPNs). JAK inhibitors ameliorate symptoms and address splenomegaly, but because of the heterogeneous contributors to the disease process, JAK inhibitor monotherapy incompletely addresses the burden of disease. The ever-growing understanding of MPN pathogenesis has provided the rationale for testing novel and targeted therapeutic agents, as monotherapies or in combination, in preclinical and clinical settings. A number of intriguing options have emerged, and it is hoped that further progress will lead to significant changes in the natural history of MPNs.

Interferon-alpha for the therapy of myeloproliferative neoplasms: targeting the malignant clone

Interferon alpha (IFN-α) has been used for over 30 years to treat myeloproliferative neoplasms (MPNs). IFN-α was shown to induce clinical, hematological, molecular and histopathological responses in small clinical studies. Such combined efficacy has never been achieved with any other drug to date in such a significant proportion of patients. However, toxicity remains a limitation to its broader use despite the development of pegylated forms with better tolerance. Several on going phase 3 studies of peg- IFN-α versus hydroxyurea will help to define its exact place in MPN management. IFN-α efficacy is likely the consequence of a broad range of biological properties, including enhancement of immune response, direct effects on malignant cells and ability to cycle dormant malignant stem cells. However, comprehensive elucidation of its mechanism of action is still lacking. Sustained clinical, molecular and morphological responses after IFN-α discontinuation raised the hope that this drug could eradicate MPN. There is now consistent evidence showing that IFN-α is able to eliminate malignant clones harboring JAK2V617F or Calreticulin mutations. However, the molecular complexity of these diseases could hamper IFN-α efficacy, as the presence of additional non-driver mutations, like in the TET2 gene, could be associated with resistance to IFN-α. Therefore, combined therapy with another targeted agent could be required to eradicate MPN, and the best IFN-α companion for achieving this challenge remains to be determined.