Low-burden TP53 mutations in chronic phase of myeloproliferative neoplasms: association with age, hydroxyurea administration, disease type and JAK2 mutational status

Multihit TP53 Mutations in Myeloproliferative Neoplasms and Acute Myeloid Leukemia: Comparative Analysis of Survival and Risk Factors in 142 Informative Cases

A total of 142 patients with myeloproliferative neoplasms (MPNs) or acute myeloid leukemia (AML) associated with multihit TP53 mutations (mTP53 MUT) were accessed from the Mayo Clinic database and included (i) chronic phase MPN (MPN-CP; N = 19), (ii) accelerated phase MPN (MPN-AP; N = 14), (iii) blast phase MPN (MPN-BP; N = 28), and (iv) AML (N = 81). Concurrent ASXL1 MUT, EZH2 MUT, IDH1,MUT and IDH2 MUT were more common in MPN-MUTBP-mTP53 compared to AML-mTP53 MUT. At median of 11.6 months follow-up, 124 (87%) deaths and 19 (13%) allogeneic stem cell transplantations (ASCT) were documented. Overall survival (OS), calculated from the time of mTP53 MUT detection, was similar between MPN-BP-mTP53 MUT (median 4.6 months) and MPN-AP-mTP53 MUT (5.6 months; p = 0.5) but both were inferior to MPN-CP-mTP53 MUT (11.6 months, p < 0.01). OS in MPN-CP-mTP53 MUT was similar to that of AML-mTP53 MUT (median 7.4 months, p = 0.07). In multivariable analysis, OS was favorably affected by ASCT (HR 0.4, p = 0.03) and disease stage (i.e., chronic phase disease) or achieving response to pre-transplant chemotherapy (HR 0.2, p < 0.01) and unfavorably by the presence of concurrent TET2 MUT or DNMT3A MUT (HR 2.7, p < 0.01). Based on these risk factors, a 3-tiered risk model was constructed: low (no risk factors; N = 18; median OS 23.8 months); intermediate (one risk factor; N = 44; 11.1 months); and high (two or more risk factors; N = 80; 4 months; p < 0.01). The current study highlights the equally detrimental impact of mTP53 MUT on long-term survival in MPN and AML and identifies predictors of short-term survival.

Potential application of the bulk RNA sequencing in routine MPN clinics

BACKGROUND

Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) are chronic hematological malignancies characterized by driver and nondriver mutations, leading to a deregulated immune system with aberrant cytokines and immune cells. Understanding the gene mutation landscape and immune state at various disease stages is crucial for guiding treatment decisions. While advanced techniques like single-cell RNA sequencing and mass cytometry provide valuable insights, their high costs and complexity limit clinical application. In contrast, bulk RNA sequencing (RNA-Seq) offers a cost-effective complementary approach for evaluating genetic mutations and immune profiles.

METHODS

Peripheral blood and bone marrow samples from treatment-naïve patients diagnosed with polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) were analyzed using RNA sequencing. Additionally, data from the microarray datasets [GSE26049, GSE2191] were included in this study. Bioinformatics methods were employed to interpret gene mutations and immune landscapes in MPN patients.

RESULTS

Our findings demonstrate the potential value of RNA-Seq in identifying gene mutations and characterizing the immune profile, including immune cell infiltration, cytokine profiles, and distinct immune-related pathways involved in the development of MPN.

CONCLUSION

Bulk RNA-Seq is a feasible tool for routine clinical practice, providing comprehensive insights into the immune and genetic landscape of MPNs. This approach could enhance personalized treatment strategies and improve prognostic accuracy, ultimately contributing to better management of MPN patients.

TP53 Mutations in Myeloproliferative Neoplasms: Context-Dependent Evaluation of Prognostic Relevance

The clinical relevance of TP53 mutations (TP53 MUT ) in myeloproliferative neoplasms (MPN) and their prognostic interaction with MPN subtype designation has not been systematically studied. In the current study, 114 patients with MPN harboring TP53 MUT (VAF ≥ 2%) were evaluated for overall survival (OS), calculated from the time of TP53 MUT detection: chronic phase myelofibrosis (MF-CP; N = 61); blast-phase (MPN-BP; N = 31) or accelerated-phase (MPN-AP; N = 16) MPN, and polycythemia vera/essential thrombocythemia (PV/ET; N = 6). Sixty-five (57%) patients harbored International Consensus Classification (ICC)-defined multihit TP53 MUT and 56 (49%) monosomal/complex karyotype (MK/CK). Majority of MPN-BP (90%) and MPN-AP (81%) while 39% of MF-CP and none of PV/ET patients harbored multihit TP53 MUT . OS in MPN-BP and MPN-AP was equally dismal (median 6 vs. 4.5 months, respectively; p = 1.0), regardless of multihit configuration (p = 0.44), while OS in TP53 MUT MPN-BP/AP (N = 47; median 4 months) was inferior to that of a separate cohort (N = 49) with TP53 wild-type MPN-BP/AP (median 11 months; p < 0.01). OS in MF-CP was significantly shorter with multihit versus non-multihit TP53 MUT (median 10 vs. 35 months; HR 2.9; p < 0.01), independent of other MF-relevant genetic risk factors, including ASXL1/SRSF2/U2AF1 mutations. Multihit TP53 MUT was also associated with inferior survival following allogeneic stem cell transplant (ASCT): median 9 months versus "not reached" in patients with (N = 9) versus without (N = 8) multihit TP53 MUT (p < 0.01). The presence of multihit or non-multihit TP53 MUT in MPN-BP/AP or multihit TP53 MUT in MF-CP is associated with exceptionally poor prognosis and justifies inclusion into the ICC category of "myeloid neoplasms with mutated TP53." By contrast, detection of non-multihit TP53 MUT, by itself, might not endanger short-term survival in MF-CP, PV, or ET.

Pathogenesis and management of high molecular risk myeloproliferative neoplasms

Classical myeloproliferative neoplasms (MPN) are clonal stem cell disorders characterized by driver mutations that affect the constitutive activation of JAK-signaling. Mutations additional to an MPN-driver occur in a large number of patients and have been shown be associated with disease presentation and progression. In this review, we outline the current hypotheses regarding how clonal evolution in MPN is thought to occur and the functional mechanisms as to how concomitant somatic mutations (i.e., mutations in genes other than the 'driver' genes) contribute to disease progression. We discuss the definitions of high molecular risk MPN, provide an overview of how concomitant mutations influence the clinical management of MPN and suggest how the rapidly developing genetic risk stratification can be utilized to improve clinical outcomes.

Unveiling the dynamics and molecular landscape of a rare chronic lymphocytic leukemia subpopulation driving refractoriness: insights from single-cell RNA sequencing

Early identification of resistant cancer cells is currently a major challenge, as their expansion leads to refractoriness. To capture the dynamics of these cells, we made a comprehensive analysis of disease progression and treatment response in a chronic lymphocytic leukemia (CLL) patient using a combination of single-cell and bulk genomic methods. At diagnosis, the patient presented with unfavorable genetic markers, including notch receptor 1 (NOTCH1) mutation and loss(11q). The initial and subsequent treatment lines did not lead to a durable response and the patient developed refractory disease. Refractory CLL cells featured substantial dysregulation in B-cell phenotypic markers such as human leukocyte antigen (HLA) genes, immunoglobulin (IG) genes, CD19 molecule (CD19), membrane spanning 4-domains A1 (MS4A1; previously known as CD20), CD79a molecule (CD79A) and paired box 5 (PAX5), indicating B-cell de-differentiation and disease transformation. We described the clonal evolution and characterized in detail two cell populations that emerged during the refractory disease phase, differing in the presence of high genomic complexity. In addition, we successfully tracked the cells with high genomic complexity back to the time before treatment, where they formed a rare subpopulation. We have confirmed that single-cell RNA sequencing enables the characterization of refractory cells and the monitoring of their development over time.

A comparative analysis of the clinical and genetic profiles of blast phase BCR::ABL1-negative myeloproliferative neoplasm and acute myeloid leukemia, myelodysplasia-related

INTRODUCTION

The classic Philadelphia chromosome-negative myeloproliferative neoplasms (Ph (-) MPNs), have variable potential for progression to the blast phase (MPN-BP) of the disease. Except initiated by distinct driver mutations, MPN-BP frequently carry similar genetic abnormalities defining acute myeloid leukemia myelodysplasia-related (AML-MR). Because of dissimilar initial pathogenesis, MPN-BP and AML-MR are retained under different disease categories. To determine if separately classifying these entities is justified, we compare MPN-BP with AML-MR patients based on mutational landscape and clinical parameters.

METHODS

104 MPN-BP patients and 145 AML-MR patients were identified with available clinical, cytogenetic, and genetic data.

RESULTS

AML-MR patients presented with a higher blast count (median, 51% vs. 30%) while MPN-BP patients had higher WBC counts, platelet counts and bone marrow cellularity (all p<0.0001). Patients with MPN-BP showed similar genetic mutations with similar mutation pattern (functional domain, hotspot and locus involved by the mutations) but a different mutation rate from AML-MR, with more frequent JAK2, CALR, MPL, ASXL1, IDH2, SETBP1 and SRSF2 mutations and less frequent TP53 and DNMT3A mutations. The overall survival (OS) of MPN-BP (OS post-BP-progression) is comparable to that of AML-MR (median OS, 9.5 months vs. 13.1 months, p=0.20). In addition, the subgroups of MPN-BP show similar OS as AML-MR. When harboring certain mutation such as TP53, ASXL1, DNMT3A, TET2, RUNX1, IDH1, IDH2, EZH2, U2AF1, BCOR and SRSF2, MPN-BP and AML-MR patients carrying the same somatic mutation show no difference in OS.

CONCLUSION

MPN-BP and AML-MR harbor similar somatic mutations and clinical outcomes, suggesting a unified clinical disease entity.

Genomic and functional impact of Trp53 inactivation in JAK2V617F myeloproliferative neoplasms

Classical myeloproliferative neoplasms (MPNs) are characterized by the proliferation of myeloid cells and the risk of transformation into myelofibrosis or acute myeloid leukemia (AML) and TP53 mutations in MPN patients are linked to AML. However, JAK2V617F has been reported to impact the TP53 response to DNA damage, suggesting potential overlapping role of TP53 inactivation in MPN. We established a mouse model showing that JAK2V617F/Vav-Cre/Trp53-/- mice displayed a similar phenotype to JAK2V617F/Vav-Cre mice, but their proliferation was outcompeted in competitive grafts. RNA-Seq revealed that half of the genes affected by JAK2V617F were affected by p53-inactivation, including the interferon pathway. To validate this finding, mice were repopulated with a mixture of wild-type and JAK2V617F (or JAK2V617F/Vav-Cre/Trp53-/-) cells and treated with pegylated interferonα. JAK2V617F-reconstituted mice entered complete hematological remission, while JAK2V617F/Vav-Cre /Trp53-/--reconstituted mice did not, confirming that p53 loss induced interferon-α resistance. KEGG and Gene Ontology analyses of common deregulated genes showed that these genes were mainly implicated in cytokine response, proliferation, and leukemia evolution, illustrating that in this mouse model, the development of MPN is not affected by TP53 inactivation. Taken together, our results show that many genetic modifications induced by JAK2V617F are influenced by TP53, the MPN phenotype may not be. Trp53 loss alone is insufficient to induce rapid leukemic transformation in steady-state hematopoiesis in JAK2V617F MPN, and Trp53 loss may contribute to interferon resistance in MPN.

The prognostic contribution of CBL, NRAS, KRAS, RUNX1, and TP53 mutations to mutation-enhanced international prognostic score systems (MIPSS70/plus/plus v2.0) for primary myelofibrosis

Contemporary risk models in primary myelofibrosis (PMF) include the mutation (MIPSS70) and mutation/karyotype enhanced (MIPSS70 plus/v2.0) international prognostic scoring systems. High molecular risk (HMR) mutations incorporated in one or both of these models include ASXL1, SRSF2, EZH2, IDH1/2, and U2AF1Q157; the current study examines additional prognostic contribution from more recently described HMR mutations, including CBL, NRAS, KRAS, RUNX1, and TP53. In a cohort of 363 informative cases (median age 58 years; 60% males), mutations included JAK2 61%, CALR 24%, MPL 6%, ASXL1 29%, SRSF2 10%, U2AF1Q157 5%, EZH2 10%, IDH1/2 4%, TP53 5%, CBL 5%, NRAS 7%, KRAS 4%, and RUNX1 4%. At a median follow-up of 4.6 years, 135 (37%) deaths and 42 (11.6%) leukemic transformations were recorded. Univariate analysis confirmed significant survival impact from the original MIPSS70/plus/v2.0 HMR mutations as well as CBL (HR 2.8; p < .001), NRAS (HR 2.4; p < .001), KRAS (HR 2.1; p = .01), and TP53 (HR 2.4; p = .004), but not RUNX1 mutations (HR 1.8; p = .08). Multivariate analysis (MVA) that included both the original and more recently described HMR mutations confirmed independent prognostic contribution from ASXL1 (HR 1.8; p = .007), SRSF2 (HR 4.3; p < .001), U2AF1Q157 (HR 2.9, p = .004), and EZH2 (HR 2.4; p < .001), but not from IDH1/2 (p = .3), TP53 (p = .2), CBL (p = .3), NRAS (p = .8) or KRAS (p = .2) mutations. The lack of additional prognostic value from CBL, NRAS, KRAS, RUNX1, and TP53 was further demonstrated in the setting of (i) MVA of mutations and karyotype, (ii) MVA of MIPSS70/plus/v2.0 composite scores and each one of the recently described HMR mutations, except TP53, and iii) modified MIPSS70/plus/plus v2.0 that included CBL, NRAS, KRAS, and TP53 as part of the HMR constituency, operationally referred to as "HMR+" category. Furthermore, "HMR+" enhancement of MIPSS70/plus/plus v2.0 did not result in improved model performance, as measured by C-statistics. We conclude that prognostic integrity of MIPSS70/plus/plus v2.0, as well as their genetic components, was sustained and their value not significantly upgraded by the inclusion of more recently described HMR mutations, including CBL, NRAS, KRAS, and RUNX1. Additional studies are needed to clarify the apparent additional prognostic value of TP53 mutation and its allelic state.

Single-cell multi-omics identifies chronic inflammation as a driver of TP53-mutant leukemic evolution

Understanding the genetic and nongenetic determinants of tumor protein 53 (TP53)-mutation-driven clonal evolution and subsequent transformation is a crucial step toward the design of rational therapeutic strategies. Here we carry out allelic resolution single-cell multi-omic analysis of hematopoietic stem/progenitor cells (HSPCs) from patients with a myeloproliferative neoplasm who transform to TP53-mutant secondary acute myeloid leukemia (sAML). All patients showed dominant TP53 'multihit' HSPC clones at transformation, with a leukemia stem cell transcriptional signature strongly predictive of adverse outcomes in independent cohorts, across both TP53-mutant and wild-type (WT) AML. Through analysis of serial samples, antecedent TP53-heterozygous clones and in vivo perturbations, we demonstrate a hitherto unrecognized effect of chronic inflammation, which suppressed TP53 WT HSPCs while enhancing the fitness advantage of TP53-mutant cells and promoted genetic evolution. Our findings will facilitate the development of risk-stratification, early detection and treatment strategies for TP53-mutant leukemia, and are of broad relevance to other cancer types.

Molecular diagnostic criteria of myeloproliferative neoplasms

INTRODUCTION

Myeloproliferative neoplasms (MPN) are a heterogeneous group of clonal hematopoietic stem cell neoplasms characterized by the driver mutations JAK2, CALR, and MPL. These mutations cause constitutive activation of JAK-STAT signaling, which is central to pathogenesis of MPNs. Next-generation sequencing has further expanded the molecular landscape allowing for improved diagnostics, prognostication, and targeted therapy.

AREAS COVERED

This review aims to address current understanding of the molecular diagnosis of MPN not only through improved awareness of the driver mutations but also the disease modifying mutations. In addition, other genetic factors such as clonal hematopoiesis of indeterminate potential (CHIP), order of mutation, and mutation co-occurrence are discussed and how these factors influence disease initiation and ultimately progression. How this molecular information is incorporated into risk stratification models allowing for earlier intervention and targeted therapy in the future will be addressed further.

EXPERT OPINION

The genomic landscape of the MPN has evolved in the last 15 years with integration of next-generation sequencing becoming the gold standard of MPN management. Although diagnostics and prognostication have become more personalized, additional studies are required to translate these molecular findings into targeted therapy therefore improving patient outcomes.

Genetic basis and molecular profiling in myeloproliferative neoplasms

BCR::ABL1-negative myeloproliferative neoplasms (MPNs) are clonal diseases originating from a single hematopoietic stem cell that cause excessive production of mature blood cells. The 3 subtypes, that is, polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are diagnosed according to the World Health Organization (WHO) and international consensus classification (ICC) criteria. Acquired gain-of-function mutations in 1 of 3 disease driver genes (JAK2, CALR, and MPL) are the causative events that can alone initiate and promote MPN disease without requiring additional cooperating mutations. JAK2-p.V617F is present in >95% of PV patients, and also in about half of the patients with ET or PMF. ET and PMF are also caused by mutations in CALR or MPL. In ∼10% of MPN patients, those referred to as being "triple negative," none of the known driver gene mutations can be detected. The common theme between the 3 driver gene mutations and triple-negative MPN is that the Janus kinase-signal transducer and activator of transcription (JAK/STAT) signaling pathway is constitutively activated. We review the recent advances in our understanding of the early events after the acquisition of a driver gene mutation. The limiting factor that determines the frequency at which MPN disease develops with a long latency is not the acquisition of driver gene mutations, but rather the expansion of the clone. Factors that control the conversion from clonal hematopoiesis to MPN disease include inherited predisposition, presence of additional mutations, and inflammation. The full extent of knowledge of the mutational landscape in individual MPN patients is now increasingly being used to predict outcome and chose the optimal therapy.

TP53 Alterations in Myelodysplastic Syndromes and Acute Myeloid Leukemia

TP53 mutations are less frequent in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) than in solid tumors, except in secondary and therapy-related MDS/AMLs, and in cases with complex monosomal karyotype. As in solid tumors, missense mutations predominate, with the same hotspot mutated codons (particularly codons 175, 248, 273). As TP53-mutated MDS/AMLs are generally associated with complex chromosomal abnormalities, it is not always clear when TP53 mutations occur in the pathophysiological process. It is also uncertain in these MDS/AML cases, which often have inactivation of both TP53 alleles, if the missense mutation is only deleterious through the absence of a functional p53 protein, or through a potential dominant-negative effect, or finally a gain-of-function effect of mutant p53, as demonstrated in some solid tumors. Understanding when TP53 mutations occur in the disease course and how they are deleterious would help to design new treatments for those patients who generally show poor response to all therapeutic approaches.

Clonal architecture evolution in Myeloproliferative Neoplasms: from a driver mutation to a complex heterogeneous mutational and phenotypic landscape

Myeloproliferative neoplasms are characterized by the acquisition at the hematopoietic stem cell level of driver mutations targeting the JAK/STAT pathway. In addition, they also often exhibit additional mutations targeting various pathways such as intracellular signalling, epigenetics, mRNA splicing or transcription. The natural history of myeloproliferative neoplasms is usually marked by a chronic phase of variable duration depending on the disease subtype, which can be followed by an accelerated phase or transformation towards more aggressive diseases such as myelofibrosis or acute leukemia. Besides, recent studies revealed important new information about the rates and mechanisms of sequential acquisition and selection of mutations in hematopoietic cells of myeloproliferative neoplasms. Better understanding of these events has been made possible in large part with the help of novel techniques that are now available to precisely decipher at the single cell level both the clonal architecture and the mutation-induced cell modifications. In this review, we will summarize the most recent knowledge about the mechanisms leading to clonal selection, how clonal architecture complexity can explain disease heterogeneity, and the impact of clonal evolution on clinical evolution.

Biological drivers of clinical phenotype in myelofibrosis

Myelofibrosis (MF) is a myeloproliferative disorder that exhibits considerable biological and clinical heterogeneity. At the two ends of the disease spectrum are the myelodepletive or cytopenic phenotype and the myeloproliferative phenotype. The cytopenic phenotype has a high prevalence in primary MF (PMF) and is characterized by low blood counts. The myeloproliferative phenotype is typically associated with secondary MF (SMF), mild anemia, minimal need for transfusion support, and normal to mild thrombocytopenia. Differences in somatic driver mutations and allelic burden, as well as the acquisition of non-driver mutations further influences these phenotypic differences, prognosis, and response to therapies such as JAK2 inhibitors. The outcome of patients with the cytopenic phenotype are comparatively worse and frequently pose a challenge to treat given the inherent exacerbation of cytopenias. Recent data indicate that an innate immune deregulated state that hinges on the myddosome-IRAK-NFκB axis favors the cytopenic myelofibrosis phenotype and offers opportunity for novel treatment approaches. We will review the biological and clinical features of the MF disease spectrum and associated treatment considerations.

Single-cell methods in myeloproliferative neoplasms: old questions, new technologies

Myeloproliferative neoplasms (MPN) are a group of clonal stem cell-derived hematopoietic malignancies driven by aberrant Janus kinase-signal transducer and activator of transcription proteins (JAK/STAT) signaling. Although these are genetically simple diseases, MPNs are phenotypically heterogeneous, reflecting underlying intratumoral heterogeneity driven by the interplay of genetic and nongenetic factors. Their evolution is determined by factors that enable certain cellular subsets to outcompete others. Therefore, techniques that resolve cellular heterogeneity at the single-cell level are ideally placed to provide new insights into MPN biology. With these insights comes the potential to uncover new approaches to predict the clinical course and treat these cancers, ultimately improving outcomes for patients. MPNs present a particularly tractable model of cancer evolution, because most patients present in an early disease phase and only a small proportion progress to aggressive disease. Therefore, it is not surprising that many groundbreaking technological advances in single-cell omics have been pioneered by their application in MPNs. In this review article, we explore how single-cell approaches have provided transformative insights into MPN disease biology, which are broadly applicable across human cancers, and discuss how these studies might be swiftly translated into clinical pathways and may eventually underpin precision medicine.

Molecular Genetics of Thrombotic Myeloproliferative Neoplasms: Implications in Precision Oncology

Classical BCR-ABL-negative myeloproliferative neoplasms (MPN) include polycythaemia vera, essential thrombocythaemia, and primary myelofibrosis. Unlike monogenic disorders, a more complicated series of genetic mutations are believed to be responsible for MPN with various degrees of thromboembolic and bleeding complications. Thrombosis is one of the early manifestations in patients with MPN. To date, the driver genes responsible for MPN include JAK2, CALR, MPL, TET2, ASXL1, and MTHFR. Affords have been done to elucidate these mutations and the incidence of thromboembolic events. Several lines of evidence indicate that mutations in JAK2, MPL, TET2 and ASXL1 gene and polymorphisms in several clotting factors (GPIa, GPIIa, and GPIIIa) are associated with the occurrence and prevalence of thrombosis in MPN patients. Some polymorphisms within XRCC1, FBG, F2, F5, F7, F12, MMP9, HPA5, MTHFR, SDF-1, FAS, FASL, TERT, ACE, and TLR4 genes may also play a role in MPN manifestation. This review aims to provide an insightful overview on the genetic perspective of thrombotic complications in patients with MPN.

Acute Myeloid Leukemia Following Myeloproliferative Neoplasms: A Review of What We Know, What We Do Not Know, and Emerging Treatment Strategies

Acute myeloid leukemia (AML) arising from myeloproliferative neoplasms (MPNs) represents a small subtype of secondary AML (sAML). This entity is well known to be associated with poor responses to available treatment options and dismal outcomes. To date, there are no standardized treatment options and there has been very little therapeutic advancement in recent years. This is a stark contrast to other subsets of AML for which there have been significant advances in therapeutic approaches, especially for patients with targetable mutations. We aim to focus our review on the incidence, risk factors for leukemogenesis, pathogenesis, molecular landscape, and emerging therapeutic options in post-myeloproliferative neoplasm acute myeloid leukemia (post-MPN AML).

BOREAS: a global, phase III study of the MDM2 inhibitor navtemadlin (KRT-232) in relapsed/refractory myelofibrosis

Patients with myelofibrosis (MF) who discontinue ruxolitinib due to progression/resistance have poor prognoses. JAK inhibitors control symptoms and reduce spleen volumes with limited impact on underlying disease pathophysiology. Murine double minute 2 (MDM2), a negative regulator of p53, is overexpressed in circulating malignant CD34+ MF cells. The oral MDM2 inhibitor navtemadlin (KRT-232) restores p53 activity to drive apoptosis of wild-type TP53 tumor cells by inducing expression of pro-apoptotic Bcl-2 family proteins. Navtemadlin demonstrated promising clinical and disease-modifying activity and acceptable safety in a phase II study in patients with relapsed/refractory MF. The randomized phase III BOREAS study compares the efficacy and safety of navtemadlin to best available therapy in patients with MF that is relapsed/refractory to JAK inhibitor treatment.

Interferons as the First Choice of Cytoreduction in Essential Thrombocythemia and Polycythemia Vera

Interferons are cytokines with immunomodulatory properties that have been used in the treatment of myeloproliferative neoplasms (MPNs) for decades. However, their widespread use has been hampered by their adverse effect profile and difficulty with administration. Recently there has been a resurgence of interest in the use of interferons in MPNs given the development of pegylated formulations with improved tolerability. Currently, treatments for polycythemia vera (PV) and essential thrombocythemia (ET) are targeted toward decreasing the risk of thrombotic complications, because there are no approved therapies that are known to modify disease. However, recent data on interferons in MPNs have suggested the potential for disease-modifying activity, including the achievement of molecular remission and sustained clinical response. This development has led to the question of whether interferons should move forward as the preferred frontline cytoreductive agent for ET and PV, and challenges the criteria currently used to initiate therapy. We review randomized controlled trial data evaluating interferon's efficacy and tolerability in patients with ET and PV. We then consider the data in the context of interferon's known advantages and disadvantages to address whether interferons should be the first choice for cytoreductive treatment in patients with ET and PV.

BMP2/SMAD pathway activation in JAK2/p53-mutant megakaryocyte/erythroid progenitors promotes leukemic transformation

Leukemic transformation (LT) of myeloproliferative neoplasm (MPN) has a dismal prognosis and is largely fatal. Mutational inactivation of TP53 is the most common somatic event in LT; however, the mechanisms by which TP53 mutations promote LT remain unresolved. Using an allelic series of mouse models of Jak2/Trp53 mutant MPN, we identify that only biallelic inactivation of Trp53 results in LT (to a pure erythroleukemia [PEL]). This PEL arises from the megakaryocyte-erythroid progenitor population. Importantly, the bone morphogenetic protein 2/SMAD pathway is aberrantly activated during LT and results in abnormal self-renewal of megakaryocyte-erythroid progenitors. Finally, we identify that Jak2/Trp53 mutant PEL is characterized by recurrent copy number alterations and DNA damage. Using a synthetic lethality strategy, by targeting active DNA repair pathways, we show that this PEL is highly sensitive to combination WEE1 and poly(ADP-ribose) polymerase inhibition. These observations yield new mechanistic insights into the process of p53 mutant LT and offer new, clinically translatable therapeutic approaches.

Analysis of the Clinical Significance and Safety of Interferon in the Treatment of Chronic Myeloproliferative Tumors

Objective

To investigate the clinical significance and safety of interferon in the treatment of chronic myeloproliferative tumors (MPN).

Methods

In this prospective study, a total of 120 patients with advanced chronic MPN admitted to our hospital between April 2016 and August 2020 were assessed for eligibility and recruited, including 62 patients with JAK2V617F mutation-positive ET (ET group) and 58 patients with JAK2V617F mutation-positive PV (PV group). 62 patients with JAK2V617F mutation-positive ET were assigned (1 : 1) to receive interferon-α (IFN-α) or hydroxyurea (HU). A similar subgrouping method for treatment of IFN-α and HU was introduced to patients with JAK2V617F mutation-positive PV. Outcome measures included efficacy and adverse reactions.

Results

For patients with JAK2V617F mutation-positive ET and PV, there were no significant differences in the overall response rate between the groups treated with IFN-α or HU (P > 0.05); however, the patients treated with IFN-α had a significantly higher 5-year progression-free survival (PFS) than those treated with HU (P < 0.05). IFN-α was associated with a significantly lower incidence of disease progression, thrombotic events, splenomegaly, myelofibrosis, nausea, and vomiting and a higher incidence of hematological adverse reactions and flu-like symptoms versus HU (P < 0.05). After six months of treatment, the PV group had 12 cases of hematological response both in the IFN-α subgroup and the HU subgroup and fewer PV patients treated with IFN-α required phlebotomy versus those treated with HU (P < 0.05), in which 4 patients in the IFN-α subgroup had no hematological response and 6 patients in the HU subgroup had no hematological response. There was no significant difference in the number of cases with phlebotomy between the two subgroups of PV patients without hematological response (P > 0.05).

Conclusion

The use of IFN in the treatment of JAK2V617F mutation-positive ET and PV patients yields a prominent clinical effect by prolonging PFS and avoiding phlebotomy for JAK2V617F mutation-positive PV patients.

Single-cell analysis reveals selection of TP53-mutated clones after MDM2 inhibition

The mechanisms of transformation of chronic myeloproliferative neoplasms (MPN) to leukemia are largely unknown, but TP53 mutations acquisition is considered a key event in this process. p53 is a main tumor suppressor, but mutations in this protein per se do not confer a proliferative advantage to the cells, and a selection process is needed for the expansion of mutant clones. MDM2 inhibitors may rescue normal p53 from degradation and have been evaluated in a variety of cancers with promising results. However, the impact of these drugs on TP53-mutated cells is underexplored. We report herein evidence of a direct effect of MDM2 inhibition on the selection of MPN patients' cells harboring TP53 mutations. To decipher whether these mutations can arise in a specific molecular context, we used a DNA single-cell approach to determine the clonal architecture of TP53-mutated cells. We observed that TP53 mutations are late events in MPN, mainly occurring in the driver clone, whereas clonal evolution frequently consists of sequential branching instead of linear consecutive acquisition of mutations in the same clone. At the single-cell level, the presence of additional mutations does not influence the selection of TP53 mutant cells by MDM2 inhibitor treatment. Also, we describe an in vitro test allowing to predict the emergence of TP53 mutated clones. Altogether, this is the first demonstration that a drug treatment can directly favor the emergence of TP53-mutated subclones in MPN.

Mutational landscape of blast phase myeloproliferative neoplasms (MPN-BP) and antecedent MPN

Myeloproliferative neoplasms (MPN) have an inherent tendency to evolve to the blast phase (BP), characterized by ≥20% myeloblasts in the blood or bone marrow. MPN-BP portends a dismal prognosis and currently, effective treatment modalities are scarce, except for allogeneic hematopoietic stem cell transplantation (allo-HSCT) in selected patients, particularly those who achieve complete/partial remission. The mutational landscape of MPN-BP differs from de novo acute myeloid leukemia (AML) in several key aspects, such as significantly lower frequencies of FLT3 and DNMT3A mutations, and higher incidence of IDH1/2 and TP53 in MPN-BP. Herein, we comprehensively review the impact of the three signaling driver mutations (JAK2 V617F, CALR exon 9 indels, MPL W515K/L) that constitutively activate the JAK/STAT pathway, and of the other somatic non-driver mutations (epigenetic, mRNA splicing, transcriptional regulators, and mutations in signal transduction genes) that cooperatively or independently promote MPN progression and leukemic transformation. The MPN subtype, harboring two or more high-molecular risk (HMR) mutations (epigenetic regulators and mRNA splicing factors) and "triple-negative" PMF are among the critical factors that increase risk of leukemic transformation and shorten survival. Primary myelofibrosis (PMF) is the most aggressive MPN; and polycythemia vera (PV) and essential thrombocythemia (ET) are relatively indolent subtypes. In PV and ET, mutations in splicing factor genes are associated with progression to myelofibrosis (MF), and in ET, TP53 mutations predict risk for leukemic transformation. The advent of targeted next-generation sequencing and improved prognostic scoring systems for PMF inform decisions regarding allo-HSCT. The emergence of treatments targeting mutant enzymes (e.g., IDH1/2 inhibitors) or epigenetic pathways (BET and LSD1 inhibitors) along with new insights into the mechanisms of leukemogenesis will hopefully lead the way to superior management strategies and outcomes of MPN-BP patients.

Genetic Background of Polycythemia Vera

Polycythemia vera belongs to myeloproliferative neoplasms, essentially by affecting the erythroblastic lineage. JAK2 alterations have emerged as major driver mutations triggering PV-phenotype with the V617F mutation detected in nearly 98% of cases. That’s why JAK2 targeting therapeutic strategies have rapidly emerged to counter the aggravation of the disease. Over decades of research, to go further in the understanding of the disease and its evolution, a wide panel of genetic alterations affecting multiple genes has been highlighted. These are mainly involved in alternative splicing, epigenetic, miRNA regulation, intracellular signaling, and transcription factors expression. If JAK2 mutation, irrespective of the nature of the alteration, is known to be a crucial event for the disease to initiate, additional mutations seem to be markers of progression and poor prognosis. These discoveries have helped to characterize the complex genomic landscape of PV, resulting in potentially new adapted therapeutic strategies for patients concerning all the genetic interferences.

Can molecular insights guide treatment of AML evolved from MPNs?

Leukemic transformation of myeloproliferative neoplasms (MPNs) is associated with dismal outcomes. The genetic complexity of leukemic transformation of MPNs is being deciphered and will likely result in targeted therapy approaches. Ongoing trials are investigating the efficacy of emerging treatments for this high-risk patient population. This review has outlined recent progress in the understanding and treatment of leukemia arising from MPNs.

Classical Philadelphia-negative myeloproliferative neoplasms (MPNs): A continuum of different disease entities

Classical Philadelphia-negative myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell-derived disorders characterized by uncontrolled proliferation of differentiated myeloid cells and close pathobiologic and clinical features. According to the 2016 World Health Organization (WHO) classification, MPNs include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The 2016 revision aimed in particular at strengthening the distinction between masked PV and JAK2-mutated ET, and between prefibrotic/early (pre-PMF) and overt PMF. Clinical manifestations in MPNs include constitutional symptoms, microvascular disorders, thrombosis and bleeding, splenomegaly secondary to extramedullary hematopoiesis, cytopenia-related symptoms, and progression to overt MF and acute leukemia. A dysregulation of the JAK/STAT pathway is the unifying mechanistic hallmark of MPNs, and is guided by somatic mutations in driver genes including JAK2, CALR and MPL. Additional mutations in myeloid neoplasm-associated genes have been also identified, with established prognostic relevance, particularly in PMF. Prognostication of MPN patients relies on disease-specific clinical models. The increasing knowledge of MPN biology led to the development of integrated clinical and molecular prognostic scores that allow a more refined stratification. Recently, the therapeutic landscape of MPNs has been revolutionized by the introduction of potent, selective JAK inhibitors (ruxolitinib, fedratinib), that proved effective in controlling disease-related symptoms and splenomegaly, yet leaving unmet critical needs, owing the lack of disease-modifying activity. In this review, we will deal with molecular, clinical, and therapeutic aspects of the three classical MPNs aiming at highlighting either shared characteristics, that overall define a continuum within a single disease family, and uniqueness, at the same time.

Genomic Profiling of a Randomized Trial of Interferon-α versus Hydroxyurea in MPN Reveals Mutation-Specific Responses

Treatment with IFNα was associated with distinct molecular responses in patients with JAK2-mutated MPN compared with CALR-mutated MPN.

Among patients treated with IFNα who did not achieve CHR, DNMT3A mutations emerged more frequently than non-DNMT3A mutations.

Although somatic mutations influence the pathogenesis, phenotype, and outcome of myeloproliferative neoplasms (MPNs), little is known about their impact on molecular response to cytoreductive treatment. We performed targeted next-generation sequencing (NGS) on 202 pretreatment samples obtained from patients with MPN enrolled in the DALIAH trial (A Study of Low Dose Interferon Alpha Versus Hydroxyurea in Treatment of Chronic Myeloid Neoplasms; #NCT01387763), a randomized controlled phase 3 clinical trial, and 135 samples obtained after 24 months of therapy with recombinant interferon-alpha (IFNα) or hydroxyurea. The primary aim was to evaluate the association between complete clinicohematologic response (CHR) at 24 months and molecular response through sequential assessment of 120 genes using NGS. Among JAK2-mutated patients treated with IFNα, those with CHR had a greater reduction in the JAK2 variant allele frequency (median, 0.29 to 0.07; P < .0001) compared with those not achieving CHR (median, 0.27 to 0.14; P < .0001). In contrast, the CALR variant allele frequency did not significantly decline in those achieving CHR or in those not achieving CHR. Treatment-emergent mutations in DNMT3A were observed more commonly in patients treated with IFNα compared with hydroxyurea (P = .04). Furthermore, treatment-emergent DNMT3A mutations were significantly enriched in IFNα–treated patients not attaining CHR (P = .02). A mutation in TET2, DNMT3A, or ASXL1 was significantly associated with prior stroke (age-adjusted odds ratio, 5.29; 95% confidence interval, 1.59-17.54; P = .007), as was a mutation in TET2 alone (age-adjusted odds ratio, 3.03; 95% confidence interval, 1.03-9.01; P = .044). At 24 months, we found mutation-specific response patterns to IFNα: (1) JAK2- and CALR-mutated MPN exhibited distinct molecular responses; and (2) DNMT3A-mutated clones/subclones emerged on treatment.

Dynamics of mutations in patients with essential thrombocythemia treated with imetelstat

In a phase II study, the telomerase inhibitor imetelstat induced rapid hematologic responses in all patients with essential thrombocythemia who were refractory to or intolerant of prior therapies. Significant molecular responses were achieved within 3-6 months in 81% of patients with phenotypic driver mutations in JAK2, CALR and MPL. Here, we investigated the dynamics of additional somatic mutations in response to imetelstat. At study entry, 50% of patients carried one to five additional mutations in the genes ASXL1, CBL, DNMT3A, EZH2, IDH1, SF3B1, TET2, TP53 and U2AF1. Three patients with baseline mutations also had late-emerging mutations in TP53, IDH1 and TET2. Most clones with additional mutations were responsive to imetelstat and decreased with the driver mutation, including the poor prognostic ASXL1, EZH2 and U2AF1 mutations, while SF3B1 and TP53 mutations were associated with poorer molecular response. Overall, phenotypic driver mutation response was significantly deeper in patients without additional mutations (P=0.04) and correlated with longer duration of response. In conclusion, this detailed molecular analysis of heavily pretreated and partly resistant patients with essential thrombocythemia reveals a high individual patient complexity. Moreover, imetelstat demonstrates potential to inhibit efficiently co-incident mutations occurring in neoplastic clones in patients with essential thrombocythemia. (ClinicalTrials.gov number, NCT01243073).

Integration of Molecular Information in Risk Assessment of Patients with Myeloproliferative Neoplasms

Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) are clonal disorders of a hematopoietic stem cell, characterized by an abnormal proliferation of largely mature cells driven by mutations in JAK2, CALR, and MPL. All these mutations lead to a constitutive activation of the JAK-STAT signaling, which represents a target for therapy. Beyond driver ones, most patients, especially with myelofibrosis, harbor mutations in an array of "myeloid neoplasm-associated" genes that encode for proteins involved in chromatin modification and DNA methylation, RNA splicing, transcription regulation, and oncogenes. These additional mutations often arise in the context of clonal hematopoiesis of indeterminate potential (CHIP). The extensive characterization of the pathologic genome associated with MPN highlighted selected driver and non-driver mutations for their clinical informativeness. First, driver mutations are enlisted in the WHO classification as major diagnostic criteria and may be used for monitoring of residual disease after transplantation and response to treatment. Second, mutation profile can be used, eventually in combination with cytogenetic, histopathologic, hematologic, and clinical variables, to risk stratify patients regarding thrombosis, overall survival, and rate of transformation to secondary leukemia. This review outlines the molecular landscape of MPN and critically interprets current information for their potential impact on patient management.

Transient expansion of TP53 mutated clones in polycythemia vera patients treated with idasanutlin

Activation of the P53 pathway through inhibition of MDM2 using nutlins has shown clinical promise in the treatment of solid tumors and hematologic malignancies. There is concern, however, that nutlin therapy might stimulate the emergence or expansion of TP53-mutated subclones. We recently published the results of a phase 1 trial of idasanutlin in patients with polycythemia vera (PV) that revealed tolerability and clinical activity. Here, we present data indicating that idasanutlin therapy is associated with expansion of TP53 mutant subclones. End-of-study sequencing of patients found that 5 patients in this trial harbored 12 TP53 mutations; however, only 1 patient had been previously identified as having a TP53 mutation at baseline. To identify the origin of these mutations, further analysis of raw sequencing data of baseline samples was performed and revealed that a subset of these mutations was present at baseline and expanded during treatment with idasanutlin. Follow-up samples were obtained from 4 of 5 patients in this cohort, and we observed that after cessation of idasanutlin, the variant allele frequency (VAF) of 8 of 9 TP53 mutations decreased. Furthermore, disease progression to myelofibrosis or myeloproliferative neoplasm blast phase was not observed in any of these patients after 19- to 32-month observation. These data suggest that idasanutlin treatment may promote transient TP53 mutant clonal expansion. A larger study geared toward high-resolution detection of low VAF mutations is required to explore whether patients acquire de novo TP53 mutations after idasanutlin therapy.

Leukemic evolution of polycythemia vera and essential thrombocythemia: genomic profiles predict time to transformation

Among myeloproliferative neoplasms, polycythemia vera (PV) and essential thrombocythemia (ET) are the 2 entities associated with the most chronic disease course. Leukemic evolution occurs rarely but has a grim prognosis. The interval between diagnosis and leukemic evolution is highly variable, from a few years to >20 years. We performed a molecular evaluation of 49 leukemic transformations of PV and ET by targeted next-generation sequencing. Using a hierarchical classification, we identified 3 molecular groups associated with a distinct time to leukemic transformation. Short-term transformations were mostly characterized by a complex molecular landscape and mutations in IDH1/2, RUNX1, and U2AF1 genes, whereas long-term transformations were associated with mutations in TP53, NRAS, and BCORL1 genes. Studying paired samples from chronic phase and transformation, we detected some mutations already present during the chronic phase, either with a significant allele burden (short-term transformation) or with a very low allele burden (especially TP53 mutations). However, other mutations were not detected even 1 year before leukemic transformation. Our results suggest that the leukemic transformation of PV and ET may be driven by distinct time-dependent molecular mechanisms.

Low-burden TP53 mutations in CLL: Clinical impact and clonal evolution within the context of different treatment options

Chronic lymphocytic leukemia (CLL) patients with TP53 mutations experience chemo-refractory disease and are therefore indicated for targeted therapy. However, the significance of low-burden TP53 mutations with <10% variant allele frequency (VAF) remains a matter of debate. Here we describe clonal evolution scenarios of low-burden TP53 mutations and analyzed their clinical impact in a "real-world" CLL cohort. TP53 status was assessed by targeted NGS in 511 patients entering first-line treatment with chemo/immunotherapy and 159 relapsed patients treated with targeted agents. Within the pre-therapy cohort, 16% of patients carried low-burden TP53 mutations (0.1-10% VAF). While their presence did not significantly shorten event-free survival after first-line therapy, it affected overall survival (OS). For a subgroup with TP53 mutations of 1-10% VAF, the impact on OS was only observed in patients with unmutated IGHV that had not received targeted therapy, as patients benefited from switching to targeted agents regardless of initial TP53 mutational status. Analysis of the clonal evolution of low-burden TP53 mutations showed that the highest expansion rates were associated with FCR in both first and second-line treatment (median VAF increase 14.8x and 11.8x, respectively) in contrast to treatment with less intense chemo/immunotherapy regimens (1.6x) and without treatment (0.8x). In the relapsed cohort, 33% of patients carried low-burden TP53 mutations, which did not expand significantly upon targeted treatment (median VAF change 1x). Sporadic cases of TP53-mut clonal shifts were connected with the development of resistance-associated mutations. Altogether, our data support the incorporation of low-burden TP53 variants in clinical decision-making.

Recent advances in prognostication and treatment of polycythemia vera

Polycythemia vera (PV) is a BCR-ABL–negative myeloproliferative neoplasm marked by acquisition of an activating mutation of JAK2, which leads to not only erythrocytosis but also frequently to leukocytosis and thrombocytosis, and is associated with a high symptom burden and increased thrombotic risk. PV has the potential to progress to myelofibrosis or an aggressive form of acute myeloid leukemia. Mutational profiling of patients with PV has led to the development of risk stratification tools to determine an individual’s risk of developing progressive disease. Although the current goals of PV treatment are to alleviate symptoms and reduce thrombotic risk, there are growing efforts to identify disease-modifying agents which will also prevent progression of disease. Here, we give an overview of the developing prognostic tools and therapeutic landscape for PV, focusing on four drug classes: pegylated interferon-alpha 2, MDM2 antagonists, hepcidin mimetics, and histone deacetylase inhibitors.

What are the molecular mechanisms driving the switch from MPNs to leukemia?

Myeloproliferative neoplasm-blast phase (MPN-BP) is a form of acute leukemia which is distinct from de novo acute myeloid leukemia with each entity being characterized by specific complex cytogenetic abnormalities and myeloid gene mutational patterns. MPN-BP patients have a particularly dismal prognosis with a medium overall survival of 5.8 months with currently available therapies. Large-scale sequencing studies have unraveled the mutational landscape of the chronic MPNs and MPN-BP, demonstrating importance of clonal heterogeneity and the role of somatic mutations in disease progression and their use to determine patient outcomes. JAK inhibitors represent the standard of care for intermediate/high-risk MF patients and have been shown to improve clinical symptoms. However, this therapeutic approach leads to a modest reduction in the variant allele frequency of the known MPN driver mutations in most patients and does not substantially delay or prevent the evolution to MPN-BP. In this article, we will review molecular mechanisms driving the progression from chronic MPNs to a BP, the impact of genetic changes on MPN-BP evolution, and the role of clonal evolution in response to JAK inhibitor therapy and disease progression. We will also discuss our ongoing functional studies of cells responsible for the development of MPN-BP.

Efficacy of ruxolitinib in a patient with myelodysplastic/myeloproliferative neoplasm unclassifiable and co-mutated JAK2, SF3B1 and TP53

Myelodysplastic/myeloproliferative neoplasm, unclassifiable (MDS/MPN-U) is a rare but heterogeneous subtype of MDS/MPN, with no specific genetic alterations and standard treatments. ASXL1, SRSF2, TET2, JAK2 and NRAS are commonly mutated in MDS/MPN-U. Double gene mutations could be detected in MDS/MPN-U, however, co-mutations of 3 and more genes in this disease entity are very rare. Here, we present a case of MDS/MPN-U with triple mutations involving JAK2, SF3B1, and TP53. After failure of traditional therapy including hydroxyurea and interferon-α, the patient received ruxolitinib monotherapy and achieved hematological response quickly. Though mutations in TP53 implied a poor prognosis in myeloid malignancies, this patient has maintained no AML transformation for 26 months since diagnosis. Further research on complex mutations in the pathogenesis and prognosis of MDS/MPN-U is warranted.

MPN: The Molecular Drivers of Disease Initiation, Progression and Transformation and their Effect on Treatment

Myeloproliferative neoplasms (MPNs) constitute a group of disorders identified by an overproduction of cells derived from myeloid lineage. The majority of MPNs have an identifiable driver mutation responsible for cytokine-independent proliferative signalling. The acquisition of coexisting mutations in chromatin modifiers, spliceosome complex components, DNA methylation modifiers, tumour suppressors and transcriptional regulators have been identified as major pathways for disease progression and leukemic transformation. They also confer different sensitivities to therapeutic options. This review will explore the molecular basis of MPN pathogenesis and specifically examine the impact of coexisting mutations on disease biology and therapeutic options.

Next Generation Sequencing in MPNs. Lessons from the Past and Prospects for Use as Predictors of Prognosis and Treatment Responses

The myeloproliferative neoplasms (MPNs) are acquired hematological stem cell neoplasms characterized by driver mutations in JAK2, CALR, or MPL. Additive mutations may appear in predominantly epigenetic regulator, RNA splicing and signaling pathway genes. These molecular mutations are a hallmark of diagnostic, prognostic, and therapeutic assessment in patients with MPNs. Over the past decade, next generation sequencing (NGS) has identified multiple somatic mutations in MPNs and has contributed substantially to our understanding of the disease pathogenesis highlighting the role of clonal evolution in disease progression. In addition, disease prognostication has expanded from encompassing only clinical decision making to include genomics in prognostic scoring systems. Taking into account the decreasing costs and increasing speed and availability of high throughput technologies, the integration of NGS into a diagnostic, prognostic and therapeutic pipeline is within reach. In this review, these aspects will be discussed highlighting their role regarding disease outcome and treatment modalities in patients with MPNs.

Leukemia secondary to myeloproliferative neoplasms

Secondary acute myeloid leukemias (AMLs) evolving from an antecedent myeloproliferative neoplasm (MPN) are characterized by a unique set of cytogenetic and molecular features distinct from de novo AML. Given the high frequency of poor-risk cytogenetic and molecular features, malignant clones are frequently insensitive to traditional AML chemotherapeutic agents. Allogeneic stem cell transplant, the only treatment modality shown to have any beneficial long-term outcome, is often not possible given the advanced age of patients at time of diagnosis and frequent presence of competing comorbidities. Even in this setting, relapse rates remain high. As a result, outcomes are generally poor and there remains a significant unmet need for novel therapeutic strategies. Although advances in cancer genomics have dramatically enhanced our understanding of the molecular events governing clonal evolution in MPNs, the cell-intrinsic and -extrinsic mechanisms driving leukemic transformation at this level remain poorly understood. Here, we review known risk factors for the development of leukemic transformation in MPNs, recent progress made in our understanding of the molecular features associated with leukemic transformation, current treatment strategies, and emerging therapeutic options for this high-risk myeloid malignancy.

Genomic heterogeneity in myeloproliferative neoplasms and applications to clinical practice

The myeloproliferative neoplasms (MPN) polycythaemia vera, essential thrombocythaemia and primary myelofibrosis are chronic myeloid disorders associated most often with mutations in JAK2, MPL and CALR, and in some patients with additional acquired genomic lesions. Whilst the molecular mechanisms downstream of these mutations are now clearer, it is apparent that clinical phenotype in MPN is a product of complex interactions, acting between individual mutations, between disease subclones, and between the tumour and background host factors. In this review we first discuss MPN phenotypic driver mutations and the factors that interact with them to influence phenotype. We consider the importance of ongoing studies of clonal haematopoiesis, which may inform a better understanding of why MPN develop in specific individuals. We then consider how best to deploy genomic testing in a clinical environment and the challenges as well as opportunities that may arise from more routine, comprehensive genomic analysis of patients with MPN.

A p53-JAK-STAT connection involved in myeloproliferative neoplasm pathogenesis and progression to secondary acute myeloid leukemia

Since the discovery of JAK2 V617F as a highly prevalent somatic acquired mutation in the majority of myeloproliferative neoplasms (MPNs), it has become clear that these diseases are driven by pathologic activation of JAK2 and eventually of STAT5 and other members of the STAT family. The concept was strengthened by the discovery of the other activating driver mutations in MPL (thrombopoietin receptor, TpoR) and in calreticulin gene, which all lead to persistent activation of wild type JAK2. Although with a rare frequency, MPNs can evolve to secondary acute myeloid leukemia (sAML), a condition that is resistant to treatment. Here we focus on the role of p53 in this transition. In sAML mutations in TP53 or amplification in genes coding for negative regulators of p53 are much more frequent than in de novo AML. We review studies that explore a signaling and biochemical interaction between activated STATs and p53 in MPNs and other cancers. With the development of advanced sequencing efforts, strong evidence has been presented for dominant negative effects of mutated p53 in leukemia. In other studies, gain of function effects have been described that might be cell type specific. A more profound understanding of the potential interaction between p53 and activated STATs is necessary in order to take full advantage of novel p53-targeted therapies.

Recent insights regarding the molecular basis of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of clonal disorders characterized by the overproduction of mature blood cells that have an increased risk of thrombosis and progression to acute myeloid leukemia. Next-generation sequencing studies have provided key insights regarding the molecular mechanisms of MPNs. MPN driver mutations in genes associated with the JAK-STAT pathway include JAK2 V617F, JAK2 exon 12 mutations and mutations in MPL, CALR, and CSF3R. Cooperating driver genes are also frequently detected and also mutated in other myeloid neoplasms; these driver genes are involved in epigenetic methylation, messenger RNA splicing, transcription regulation, and signal transduction. In addition, other genetic factors such as germline predisposition, order of mutation acquisition, and variant allele frequency also influence disease initiation and progression. This review summarizes the current understanding of the genetic basis of MPN, and demonstrates how molecular pathophysiology can improve both our understanding of MPN heterogeneity and clinical practice.

The poor outcome in high molecular risk, hydroxycarbamide-resistant/intolerant ET is not ameliorated by ruxolitinib

Essential Thrombocythemia (ET) patients at high-risk of thrombosis require cytoreductive treatment, typically with hydroxycarbamide. Many patients are resistant or intolerant to hydroxycarbamide (HC-RES/INT) and are at increased risk of disease progression. MAJIC-ET is a randomized phase 2 study comparing ruxolitinib (RUX) to best available therapy (BAT) in HC-RES/INT ET, which showed no difference between the two arms in rates of hematological response or disease progression. The impact of additional non-MPN driver mutations (NDM) on the risk of disease complications in HC-RES/INT ET patients is unknown. Since the presence of NDM may influence trial outcomes, we expand the primary MAJIC-ET analysis to serially evaluate NDM in MAJIC-ET patients using a targeted myeloid 32-gene panel. NDM at baseline were detected in 30% of patients, most frequently affecting TET2 (11%) followed by TP53 (6.4%) and SF3B1 (6.4%). The presence of a NDM was associated with inferior 4-year transformation-free survival (TFS; 65.4% [95% CI 53.3 – 75%] vs. 82.8% [95% CI 73.2 – 89.1%], p=0.017). Specifically, TP53 (p=0.01) and splicing factor (SF, SF3B1, ZRSR2, SRSF2 ; p<0.001), but not TET2 mutations were associated with reduced TFS which was not mitigated by RUX treatment. Longitudinal analysis identified new mutations in 19.3% of patients; primarily affecting TET2, TP53 and SF3B1 . We report the first comprehensive mutational analysis of HC-RES/INT ET patients and highlight the clinical/prognostic utility of serial mutation analysis for NDM in HC-RES/INT ET, including the importance of SF and TP53 mutations which identify HC-RES/INT ET patients at increased risk of disease transformation.

Advanced forms of MPNs are accompanied by chromosomal abnormalities that lead to dysregulation of TP53

The Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), including polycythemia vera (PV), essential thrombocythemia (ET), and the prefibrotic form of primary myelofibrosis (PMF), frequently progress to more overt forms of MF and a type of acute leukemia termed MPN-accelerated phase/blast phase (MPN-AP/BP). Recent evidence indicates that dysregulation of the tumor suppressor tumor protein p53 (TP53) commonly occurs in the MPNs. The proteins MDM2 and MDM4 alter the cellular levels of TP53. We investigated in 1,294 patients whether abnormalities involving chromosomes 1 and 12, which harbor the genes for MDM4 and MDM2, respectively, and chromosome 17, where the gene for TP53 is located, are associated with MPN disease progression. Gain of 1q occurred not only in individuals with MPN-BP but also in patients with PV and ET, who, with further follow-up, eventually evolve to either MF and/or MPN-BP. These gains of 1q were most prevalent in patients with a history of PV and those who possessed the JAK2V617F driver mutation. The gains of 1q were accompanied by increased transcript levels of MDM4 In contrast, 12q chromosomal abnormalities were exclusively detected in patients who presented with MF or MPN-BP, but were not accompanied by further increases in MDM2/MDM4 transcript levels. Furthermore, all patients with a loss of 17p13, which leads to a deletion of TP53, had either MF or MPN-AP/BP. These findings suggest that gain of 1q, as well as deletions of 17p, are associated with perturbations of the TP53 pathway, which contribute to MPN disease progression.

Oral idasanutlin in patients with polycythemia vera

A limited number of drugs are available to treat patients with polycythemia vera (PV) and essential thrombocythemia (ET). We attempted to identify alternative agents that may target abnormalities within malignant hematopoietic stem (HSCs) and progenitor cells (HPCs). Previously, MDM2 protein levels were shown to be upregulated in PV/ET CD34⁺ cells, and exposure to a nutlin, an MDM2 antagonist, induced activation of the TP53 pathway and selective depletion of PV HPCs/HSCs. This anticlonal activity was mediated by upregulation of p53 and potentiated by the addition of interferon-α2a (IFN-α2a). Therefore, we performed an investigator-initiated phase 1 trial of the oral MDM2 antagonist idasanutlin (RG7388; Roche) in patients with high-risk PV/ET for whom at least 1 prior therapy had failed. Patients not attaining at least a partial response by European LeukemiaNet criteria after 6 cycles were then allowed to receive combination therapy with low-dose pegylated IFN-α2a. Thirteen patients with JAK2 V617F⁺ PV/ET were enrolled, and 12 (PV, n = 11; ET, n = 1) were treated with idasanutlin at 100 and 150 mg daily, respectively, for 5 consecutive days of a 28-day cycle. Idasanutlin was well tolerated; no dose-limiting toxicity was observed, but low-grade gastrointestinal toxicity was common. Overall response rate after 6 cycles was 58% (7 of 12) with idasanutlin monotherapy and 50% (2 of 4) with combination therapy. Median duration of response was 16.8 months (range, 3.5-26.7). Hematologic, symptomatic, pathologic, and molecular responses were observed. These data indicate that idasanutlin is a promising novel agent for PV; it is currently being evaluated in a global phase 2 trial. This trial was registered at www.clinicaltrials.gov as #NCT02407080.