Clinical impact of mutated JAK2 allele burden reduction in polycythemia vera and essential thrombocythemia.

The variant allele frequency (VAF) of driver mutations (JAK2, CALR) in myeloproliferative neoplasms is associated with features of advanced disease and complications. Ruxolitinib and interferon were reported to variably reduce the mutant VAF, but the long-term impact of molecular responses (MR) remains debated. We prospectively measured changes in JAK2 and CALR VAF in 77 patients with polycythemia vera and essential thrombocythemia, treated with ruxolitinib for a median of 8 years, and assessed correlation with complete clinical and hematological response (CCHR) and outcomes. At last observation time, JAK2 VAF reduced overall from a median of 68% (range, 20%-99%) to 3.5% (0%-98%). A profound and durable MR (DMR; defined as a VAF stably ≤2%), including complete MR in 8%, was achieved in 20% of the patients, a partial MR (PMR; VAF reduction >50% of the baseline level) in 25%, and 56% had no molecular response (NMR). A CCHR was reached by 69% overall, independently of any degree of MR achieved; conversely, a DMR correlated with longer duration of CCHR and, most importantly, with reduced rate of progression to myelofibrosis and with longer myelofibrosis-free, event-free and progression-free survival. Achievement of PMR also had some favorable impact on outcomes, compared to NMR. A baseline JAK2 VAF <50%, and a VAF reduction of ≥35% after 2 years of treatment, predicted for the achievement of DMR and reduced progression to myelofibrosis. Overall, these findings support the clinical value of achieving profound, durable MR and its consideration as surrogate endpoint in future clinical trials.

Bosutinib Treatment of Chronic Myeloid Leukemia in Lombardy.

INTRODUCTION: Up to 30% of CML patients will require a therapeutic change during follow-up due to intolerance and/or resistance to first-line tyrosine kinase inhibitor (TKI) approach. In this context, bosutinib (BOS) has not only demonstrated its efficacy, but also presents a favorable safety profile, without comorbid conditions representing an absolute contraindication to its use. METHODS: To gain further into BOS treatment in real life, we conducted a retrospective analysis on the outcome of CML patients receiving BOS in 18 hematological centers, all belonging to the "REL" (Lombard Hematology Network). RESULTS: Of 546 regularly followed CML cases, a total of 132 patients were reported as being treated with BOS, most frequently (62.9%) in second line. Interestingly, most patients (63.6%) switched to BOS due to intolerance to the previous TKI, while resistance to the last treatment was reported in the remaining 36.4% of patients. Despite a permanent discontinuation rate of 18.9%, over 80% of patients achieved at least a major molecular response and seven cases were able to attempt treatment-free remission. CONCLUSION: Although in this survey BOS represented the preferred option especially in patients intolerant rather than resistant to previous TKIs, we confirmed that BOS represents a safe and effective therapeutic option beyond the first line in the real-life setting.

Risk of progression in chronic phase-chronic myeloid leukemia patients eligible for tyrosine kinase inhibitor discontinuation: Final analysis of the TFR-PRO study.

Disease progression to accelerated/blast phase (AP/BP) in patients with chronic phase chronic myeloid leukemia (CP-CML) after treatment discontinuation (TD) has never been systematically reported in clinical trials. However, recent reports of several such cases has raised concern. To estimate the risk of AP/BP among TD-eligible patients, we conducted TFR-PRO, a cohort retro-prospective study: 870 CP-CML patients eligible for TD formed a discontinuation cohort (505 patients) and a reference one (365 patients). The primary objective was the time adjusted rate (TAR) of progression in relation to TD. Secondary endpoints included the TAR of molecular relapse, that is, loss of major molecular response (MMR). With a median follow up of 5.5 years and 5188.2 person-years available, no events occurred in the TD cohort. One event of progression was registered 55 months after the end of TD, when the patient was contributing to the reference cohort. The TAR of progression was 0.019/100 person-years (95% CI [0.003-0.138]) in the overall group; 0.0 (95% CI [0-0.163]) in the discontinuation cohort; and 0.030 (95% CI [0.004-0.215]) in the reference cohort. These differences are not statistically significant. Molecular relapses occurred in 172/505 (34.1%) patients after TD, and in 64/365 (17.5%) patients in the reference cohort, p < .0001. Similar rates were observed in TD patients in first, second or third line of treatment. CML progression in patients eligible for TD is rare and not related to TD. Fears about the risk of disease progression among patients attempting TD should be dissipated.

Comparing the safety and efficacy of ruxolitinib in patients with Dynamic International Prognostic Scoring System low-, intermediate-1-, intermediate-2-, and high-risk myelofibrosis in JUMP, a Phase 3b, expanded-access study.

Ruxolitinib, a potent Janus kinase 1/2 inhibitor, has demonstrated durable improvements in patients with myelofibrosis. In this analysis of the Phase 3b JUMP study, which included patients aged ≥18 years with a diagnosis of primary or secondary myelofibrosis, we assessed the safety and efficacy of ruxolitinib in patients stratified by Dynamic International Prognostic Scoring System (DIPSS) risk categories. Baseline characteristic data were available to assess DIPSS status for 1844 of the 2233 enrolled patients; 60, 835, 755, and 194 in the low-, intermediate (Int)-1-, Int-2-, and high-risk groups, respectively. Ruxolitinib was generally well tolerated across all risk groups, with an adverse-event (AE) profile consistent with previous reports. The most common hematologic AEs were thrombocytopenia and anemia, with highest rates of Grade ≥3 events in high-risk patients. Approximately, 73% of patients experienced ≥50% reductions in palpable spleen length at any point in the ≤24-month treatment period, with highest rates in lower-risk categories (low, 82.1%; Int-1, 79.3%; Int-2, 67.1%; high risk, 61.6%). Median time to spleen length reduction was 5.1 weeks and was shortest in lower-risk patients. Across measures, 40%-57% of patients showed clinically meaningful symptom improvements, which were observed from 4 weeks after treatment initiation and maintained throughout the study. Overall survival (OS) was 92% at Week 72 and 75% at Week 240 (4.6 years). Median OS was longer for Int-2-risk than high-risk patients (253.6 vs. 147.3 weeks), but not evaluable in low-/Int-1-risk patients. By Week 240, progression-free survival (PFS) and leukemia-free survival (LFS) rates were higher in lower-risk patients (PFS: low, 90%; Int-1, 82%; Int-2, 46%; high risk, 15%; LFS: low, 92%; Int-1, 86%; Int-2, 58%; high risk, 19%). Clinical benefit was seen across risk groups, with more rapid improvements in lower risk patients. Overall, this analysis indicates that ruxolitinib benefits lower-risk DIPSS patients in addition to higher risk.

The role of JAK2 inhibitors in MPNs 7 years after approval.

Myeloproliferative neoplasms (MPNs) include essential thrombocythemia, polycythemia vera (PV), and primary myelofibrosis (MF). Phenotype-driver mutations of JAK2, CALR, and MPL genes are present in MPNs and can be variably combined with additional mutations. Driver mutations entail a constitutive activation of the JAK2/STAT pathway, the key signaling cascade in MPNs. Among JAK2 inhibitors (JAKis), ruxolitinib (RUX) has been approved for the treatment of intermediate and high-risk MF and for PV inadequately controlled by or intolerant of hydroxyurea. Other JAKis, such as fedratinib and pacritinib, proved to be useful in MF. The primary end points in MF trials were spleen volume response (SVR) and symptom response, whereas in PV trials they were hematocrit control with or without spleen response. In advanced MF, RUX achieved a long lasting SVR of >35% in ∼60% of patients, establishing a new benchmark for MF treatment. RUX efficacy in early MF is also remarkable and toxicity is mild. In PV, RUX achieved hematocrit control in ∼60% of cases and SVR in 40%. Symptom relief was evident in both conditions. In the long-term, however, many MF patients lose their SVR. Indeed, the definition of RUX failure and the design of new trials in this setting are unmet needs. Decrease of hemoglobin/platelet levels and increased infection rates are the most common side effects of RUX, and nonmelanoma skin tumors need to be monitored while on treatment. In conclusion, the introduction of JAKis raises the bar of treatment goals in MF and PV.

Myeloproliferative and lymphoproliferative disorders: State of the art.

Myeloproliferative neoplasms (MPNs), including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are clonal disorders complicated mainly by vascular events and transformation to myelofibrosis (for PV and ET) or leukemia. Although secondary malignancies, in particular, lymphoproliferative disorders (LPNs), are rare, they occur at a higher frequency than found in the general population, and there has been recent scientific discussion regarding a hypothetical relationship between treatment with JAK inhibitors in MPN and the risk of development of LPN. This has prompted increased interest regarding the coexistence of MPN and LPN. This review focuses on the role of JAK2 and the JAK/STAT pathway in MPN and LPN, whether there is a role for the genetic background in the occurrence of both MPN and LPN and whether there is a role for cytoreductive drugs in the occurrence of both MPN and LPN. Furthermore, whether an increased risk of lymphoma development is limited to patients who receive the JAK inhibitor ruxolitinib, is a more general phenomenon that occurs following JAK1/2 inhibition or is associated with preferential JAK1 or JAK2 targeting is discussed.

Tracing the decision-making process for myelofibrosis: diagnosis, stratification, and management of ruxolitinib therapy in real-word practice.

The management of patients with myelofibrosis (MF) has dramatically changed since the introduction of ruxolitinib as a tailored treatment strategy. However, the perceptions about the use of this drug in clinical practice remain, at times, a matter of discussion. We conducted a survey about the diagnostic evaluation, prognostic assessment, and management of ruxolitinib in real-life clinical practice in 18 Italian hematology centers. At diagnosis, most hematologists do not use genetically or molecularly inspired score systems to assess prognosis, mainly due to scarce availability of next-generation sequencing (NGS) methodology, with NGS conversely reserved only for a subset of lower-risk MF patients with the aim of possibly improving the treatment strategy. Some common points in the management of ruxolitinib were 1) clinical triggers for ruxolitinib therapy, regardless of risk category; 2) evaluation of infectious risk before the starting of the drug; and 3) schedule of monitoring during the first 12 weeks with the need, in some instances, of supportive treatment. Further development of international recommendations and insights will allow the achievement of common criteria for the management of ruxolitinib in MF, before and after treatment, and for the definition of response and failure.

Presentation and outcome of patients with 2016 WHO diagnosis of prefibrotic and overt primary myelofibrosis.

The 2016 revision of the World Health Organization (WHO) classification of myeloproliferative neoplasms defines 2 stages of primary myelofibrosis (PMF): prefibrotic/early (pre-PMF) and overt fibrotic (overt PMF) phase. In this work, we studied the clinical and molecular features of patients belonging to these categories of PMF. The diagnosis of 661 PMF patients with a bone marrow biopsy at presentation was revised according to modern criteria; clinical information and annotation of somatic mutations in both driver and selected nondriver myeloid genes were available for all patients. Compared with pre-PMF, overt PMF was enriched in patients with anemia, thrombocytopenia, leukopenia, higher blast count, symptoms, large splenomegaly, and unfavorable karyotype. The different types of driver mutations were similarly distributed between the 2 categories, whereas selected mutations comprising the high mutation risk (HMR) category (any mutations in ASXL1, SRSF2, IDH1/2, EZH2) were more represented in overt PMF. More patients with overt PMF were in higher International Prognostic Scoring System risk categories at diagnosis, and the frequency increased during follow-up, suggesting greater propensity to disease progression compared with pre-PMF. Median survival was significantly shortened in overt PMF (7.2 vs 17.6 years), with triple negativity for driver mutations and presence of HMR mutations representing independent predictors of unfavorable outcome. The findings of this "real-life" study indicate that adherence to 2016 WHO criteria allows for identification of 2 distinct categories of patients with PMF where increased grades of fibrosis are associated with more pronounced disease manifestations, adverse mutation profile, and worse outcome, overall suggesting they might represent a phenotypic continuum.

Treating early-stage myelofibrosis.

Myelofibrosis (MF) is a Philadelphia chromosome-negative myeloproliferative neoplasm associated with bone marrow fibrosis, splenomegaly, a high symptom burden, and poor prognosis. Treatment is based on a risk-adapted approach, with treatment guidelines generally recommending allogeneic stem cell transplant or drug-based therapy for patients with higher-risk or more advanced disease and recommending observation or the "watch-and-wait" strategy for those with lower-risk or early-stage MF. With the advent of targeted therapies, such as the Janus kinase inhibitors, many patients have experienced substantial clinical benefits, including reduction in splenomegaly and symptoms and, in some instances, improvement or stabilization of bone marrow fibrosis and reduction of JAK2 V617F allele burden. These observations raise the possibility of patients in earlier phases of the disease also benefiting from treatment with targeted therapies. In this review, we discuss the current treatment options for patients with early-stage MF and the available evidence supporting the treatment of patients with less-advanced disease. Overall, therapies used to treat patients with early-stage MF will have to be assessed in randomized studies, with the potential benefits balanced against adverse events associated with treatment.

Life for patients with myelofibrosis: the physical, emotional and financial impact, collected using narrative medicine-Results from the Italian 'Back to Life' project.

PURPOSE: Myelofibrosis (MF) is a chronic myeloproliferative neoplasm characterised by an aggressive clinical course, with disabling symptoms and reduced survival. Patients experience a severely impaired quality of life and their families face the upheaval of daily routines and high disease-related financial costs. The aim of this study was to investigate the perceptions of Italian patients and their caregivers about living with MF and the burden of illness associated with MF. METHODS: A quali-quantitative questionnaire and a prompted written narrative survey were administered to patients affected by primary or post-essential thrombocythemia/post-polycythaemia vera MF and their primary caregiver in 35 Italian haematological centres. RESULTS: In total, 287 questionnaires were returned by patients and 98 by caregivers, with 215 and 62, respectively, including the narrative. At the time of diagnosis, the most commonly expressed emotional states of patients were fear, distress and anger, confirming the difficulty of this phase. A high level of emotional distress was also reported by caregivers. Along the pathway of care, the ability to cope with the disease differed according to the quality of care received. The mean cost to each patient attributable to MF was estimated as €12,466 per year, with an estimated average annual cost of loss of income of €7774 per patient and €4692 per caregiver. CONCLUSIONS: Better understanding of the personal life of MF patients and their families could improve the relationships between health workers and patients, resulting in better focused healthcare pathways and more effective financial support to maintain patients in their social roles.

Impact of allogeneic stem cell transplantation on survival of patients less than 65 years of age with primary myelofibrosis.

Allogeneic hematopoietic stem cell transplantation (SCT) is the only curative option for patients with primary myelofibrosis (PMF), but information on its net advantage over conventional therapies is lacking. Using ad hoc statistical analysis, we determined outcomes in 438 patients <65 years old at diagnosis who received allogenic SCT (n = 190) or conventional therapies (n = 248). Among patients at low risk per the Dynamic International Prognostic Scoring System (DIPSS) model, the relative risk of death after allogenic SCT vs those treated with nontransplant modalities was 5.6 (95% CI, 1.7-19; P = .0051); for intermediate-1 risk it was 1.6 (95% CI, 0.79-3.2; P = .19), for intermediate-2 risk, 0.55 (95% CI, 0.36-0.83; P = .005), and for high risk, 0.37 (95% CI, 0.21-0.66; P = .0007). Thus, patients with intermediate-2 or high-risk PMF clearly benefit from allogenic SCT. Patients at low risk should receive nontransplant therapy, whereas individual counseling is indicated for patients at intermediate-1 risk.

Polycythemia vera: from new, modified diagnostic criteria to new therapeutic approaches.

Polycythemia vera (PV) is a Philadelphia chromosome-negative chronic myeloproliferative neoplasm that is associated with a Janus kinase 2 (JAK2) mutation in most cases. The most recent update to the World Health Organization diagnostic criteria for PV was published in 2016. These were the modifications with the greatest effect: (1) lowering the hemoglobin threshold, allowing a diagnosis of PV at 16.5 g/dL in males and at 16.0 g/dL in females and (2) introducing a hematocrit cutoff (49% in males and 48% in females). Patients with PV who are older than 60 years or have had a previous thrombotic event are considered at high risk for thrombosis. Leukocytosis and a high allele burden are additional risk factors for thrombosis and myelofibrosis, respectively. After disease has progressed to post-polycythemia vera myelofibrosis (PPV-MF), survival must be assessed according to the recently developed Myelofibrosis Secondary to PV and ET-Prognostic Model (MYSEC-PM). This model is based on age at diagnosis, a hemoglobin level below 11 g/dL, a platelet count lower than 150 × 109/L, a percentage of circulating blasts of 3% or higher, a CALR-unmutated genotype, and the presence of constitutional symptoms. Therapy is based on phlebotomy to maintain the hematocrit below 45% and (if not contraindicated) aspirin. When a cytoreductive drug is necessary, hydroxyurea or interferon can be used as first-line therapy, although the demonstration of an advantage of interferon over hydroxyurea is still pending. In patients whose disease fails to respond to hydroxyurea, ruxolitinib is a safe and effective choice.

New molecular genetics in the diagnosis and treatment of myeloproliferative neoplasms.

PURPOSE OF REVIEW: Myeloproliferative neoplasms (MPN) are conditions of great interest because of the identification of their molecular basis and of the entering of new small molecules into clinical practice. The aim of this review is to report the role of mutations in the diagnosis, prognosis, and in the prediction of response to JAK inhibitors in MPN. RECENT FINDINGS: New mutations of the CALR gene have been discovered in patients without JAK2 or MPL mutations and are now included in the World Health Organization classification system. The role of ASXL1 and SRSF2 together with the driver mutations is emerging in the prognostication of myelofibrosis. SUMMARY: A wide mutational analysis of MPN helps to define diagnosis and prognosis. In the future, clinical trials based on a robust valuation of mutations will guide treatment decision-making towards precision medicine.

Impact of ruxolitinib on the natural history of primary myelofibrosis: a comparison of the DIPSS and the COMFORT-2 cohorts.

The international prognostic scoring system (IPSS) provides reliable risk assessment in patients with primary myelofibrosis (PMF). Recent clinical trials in PMF patients with intermediate-2 or high IPSS risk have shown a survival advantage of ruxolitinib over placebo (COMFORT-1) or best available therapy (COMFORT-2). Because crossover was allowed in these studies, we analyzed the cohort of ruxolitinib-naive patients used for developing the dynamic IPSS (DIPSS). By adopting ad hoc statistical analyses, we compared survival from diagnosis of 100 PMF patients receiving ruxolitinib within COMFORT-2 with that of 350 patients of the DIPSS study. Subjects were properly matched, and both left-truncation and right-censoring were accounted in order to compare higher IPSS risks exclusively. Patients receiving ruxolitinib had longer survival (5 years, 95% confidence interval [CI]: 2.9-7.8 vs 3.5 years, 95% CI: 3.0-3.9) with a hazard ratio of 0.61 (95% CI: 0.41-0.91; P = .0148). This observation suggests that ruxolitinib may modify the natural history of PMF.

Epidemiology and clinical relevance of mutations in postpolycythemia vera and postessential thrombocythemia myelofibrosis: A study on 359 patients of the AGIMM group.

Transformation to secondary myelofibrosis (MF) occurs as part of the natural history of polycythemia vera (PPV-MF) and essential thrombocythemia (PET-MF). Although primary (PMF) and secondary MF are considered similar diseases and managed similarly, there are few studies specifically focused on the latter. The aim of this study was to characterize the mutation landscape, and describe the main clinical correlates and prognostic implications of mutations, in a series of 359 patients with PPV-MF and PET-MF. Compared with PV and ET, the JAK2V617F and CALR mutated allele burden was significantly higher in PPV-MF and/or PET-MF, indicating a role for accumulation of mutated alleles in the process of transformation to MF. However, neither the allele burden nor the type of driver mutation influenced overall survival (OS), while absence of any driver mutation (triple negativity) was associated with significant reduction of OS in PET-MF, similar to PMF. Of the five interrogated subclonal mutations (ASXL1, EZH2, SRSF2, IDH1, and IDH2), that comprise a prognostically detrimental high molecular risk (HMR) category in PMF, only SRSF2 mutations were associated with reduced survival in PET-MF, and no additional mutation profile with prognostic relevance was highlighted. Overall, these data indicate that the molecular landscape of secondary forms of MF is different from PMF, suggesting that unknown mutational events might contribute to the progression from chronic phase disease to myelofibrosis. These findings also support more extended genotyping approaches aimed at identifying novel molecular abnormalities with prognostic relevance for patients with PPV-MF and PET-MF. Am. J. Hematol. 91:681-686, 2016. © 2016 Wiley Periodicals, Inc.

Prognostic impact of bone marrow fibrosis in primary myelofibrosis. A study of the AGIMM group on 490 patients.

The prognostic significance of bone marrow (BM) fibrosis grade in patients with primary myelofibrosis (PMF) is still debated. A fibrosis grade greater than 1 was shown to associate with higher risk of death, and addition of fibrosis grade to IPSS score resulted in a more accurate prediction of survival. The aim of this study was to analyze the prognostic impact of BM fibrosis in 490 patients with PMF, evaluated at diagnosis, molecularly annotated and with extensive follow-up information. We found that fibrosis grade 2 and greater on a 0-3 scale was associated with clinical characteristics indicative of a more advanced disease, such as anemia, leukopenia, thrombocytopenia, constitutional symptoms, larger splenomegaly and a higher IPSS risk category. Patients with higher grade of fibrosis were also more likely to have additional somatic mutations in ASXL1 and EZH2, that are prognostically adverse. Median survival was significantly reduced in patients with grade 2 and 3 fibrosis as compared with grade 1; this effect was maintained when analysis was restricted to younger patients. In multivariate analysis, fibrosis grade independently predicted for survival regardless of IPSS variables and mutational status; the adverse impact of fibrosis was noticeable especially in lower IPSS risk categories. Overall, results indicate that higher grades of fibrosis correlate with unique clinical and molecular aspects and represent an independent adverse variable in patients with PMF; these observations deserve confirmation in prospectively designed series of patients. Am. J. Hematol. 91:918-922, 2016. © 2016 Wiley Periodicals, Inc.

Personal history and quality of life in chronic myeloid leukemia patients: a cross-sectional study using narrative medicine and quantitative analysis.

BACKGROUND: Tyrosine kinase inhibitors (TKIs) drastically changed the outcome of patients diagnosed with chronic myeloid leukemia (CML). Several reports indicated the advantage of continue long-term adherence associated with positive outcome. Therefore, it is important to better understand from the patient's standpoint the experience of living with the disease and the related treatment. OBJECTIVES: In this study, quantitative analysis and narrative medicine were combined to get insights on this issue in a population of 257 patients with CML in chronic phase treated with TKIs (43 % men, with a median age of 58 years, 27 % aged 31-50 years), followed for a median time of 5 years. Sixty-one percent of patients enrolled were treated in first line, whereas 37 % were treated in second line. RESULTS: The results showed more positive perceptions and acceptance in males compared to females, without impact of disease on relationships. Level of positive acceptance was more evident in elderly compared to younger patients, with a close connection with median time from diagnosis. Overall, female patients reported negative perceptions and an impact of disease on family daily living. The majority of patients understood the importance of continue adherence to treatment, with 27 % resulting less adherent (60 % for forgetfulness), even if well informed and supported by his/her physician. DISCUSSION AND CONCLUSIONS: Narrative medicine, in association to quantitative analysis, can help physicians to understand needs of their patients in order to improve communication.

Mutations and thrombosis in essential thrombocythemia: prognostic interaction with age and thrombosis history.

BACKGROUND: Vascular events in essential thrombocythemia (ET) are associated with advanced age and thrombosis history. Recent information suggests additional effect from the presence of specific mutations. OBJECTIVES: To examine the influence of age and thrombosis history on the reported association between mutational status and thrombosis-free survival in ET. PATIENTS AND METHODS: Analysis was performed using a Mayo Clinic cohort of 300 ET patients, and key findings were reanalyzed by including additional 102 Italian patients. RESULTS: Among 300 Mayo patients with ET (median age 55 yr, 60% females), mutational frequencies were 53% JAK2, 32% CALR, 3% MPL, and 12% JAK2, CALR and MPL wild type. One hundred and six (35%) patients experienced arterial (n = 75) or venous (n = 43) events, before (n = 55) or after (n = 71) diagnosis. In univariate analysis, compared to JAK2-mutated cases, JAK2, CALR and MPL wild type (HR 0.31, 95% CI 0.11-0.86), and CALR-mutated (0.53, 95% CI 0.30-0.92) patients displayed better thrombosis-free survival. JAK2, CALR, and MPL wild type remained significant (P = 0.03; HR 0.32, 95% CI 0.11-0.9) during multivariable analysis that included age (P = 0.01) and thrombosis history (P = 0.0006); a favorable impact from CALR mutations was of borderline significance (P = 0.1; HR 0.62, 95% CI 0.35-1.1), but became significant (P = 0.02) when multivariable analysis including thrombosis history (P = 0.02) was performed on patients younger than 60 yr of age. CONCLUSIONS: The favorable impact of mutational status on thrombosis-free survival in ET might be most evident for JAK2, CALR, and MPL wild type patients, whereas the favorable effect from CALR mutations might be confined to young patients.