Clinical significance of chromatin-spliceosome acute myeloid leukemia: a report from the Northern Italy Leukemia Group (NILG) randomized trial 02/06.

Secondary acute myeloid leukemia (sAML) after myelodysplastic or myeloproliferative disorders is a high-risk category currently identified by clinical history or specific morphological and cytogenetic abnormalities. However, in the absence of these features, uncertainties remain to identify the secondary nature of some cases otherwise defined as de novo AML. To test whether a chromatin-spliceosome (CS) mutational signature might better inform the definition of the de novo AML group, we analyzed a prospective cohort of 413 newly diagnosed AML patients enrolled into a randomized clinical trial (NILG AML 02/06) and provided with accurate cytogenetic and molecular characterization. Among clinically defined de novo AML, 17.6% carried CS mutations (CS-AML) and showed clinical characteristics closer to sAML (older age, lower white blood cell counts and higher rate of multilineage dysplasia). Outcomes in this group were adverse, more similar to those of sAML as compared to de novo AML (overall survival, 30% in CS-AML and 17% in sAML vs 61% in de novo AML, P<0.0001; disease free survival, 26% in CS-AML and 22% in sAML vs 54% of de novo AML, P<0.001) and independently confirmed by multivariable analysis. Allogeneic transplant in first complete remission improved survival in both sAML and CS-AML patients. In conclusion, these findings highlight the clinical significance of identifying CS-AML for improved prognostic prediction and potential therapeutic implications. (NILG AML 02/06: ClinicalTrials.gov Identifier: NCT00495287).

Splanchnic vein thromboses associated with myeloproliferative neoplasms: An international, retrospective study on 518 cases.

Myeloproliferative Neoplasms (MPN) course can be complicated by thrombosis involving unusual sites as the splanchnic veins (SVT). Their management is challenging, given their composite vascular risk. We performed a retrospective, cohort study in the framework of the International Working Group for MPN Research and Treatment (IWG-MRT), and AIRC-Gruppo Italiano Malattie Mieloproliferative (AGIMM). A total of 518 MPN-SVT cases were collected and compared with 1628 unselected, control MPN population, matched for disease subtype. Those with MPN-SVT were younger (median 44 years) and enriched in females compared to controls; PV (37.1%) and ET (34.4%) were the most frequent diagnoses. JAK2V617F mutation was highly prevalent (90.2%), and 38.6% of cases had an additional hypercoagulable disorder. SVT recurrence rate was 1.6 per 100 patient-years. Vitamin K-antagonists (VKA) halved the incidence of recurrence (OR 0.48), unlike cytoreduction (OR 0.96), and were not associated with overall or gastrointestinal bleeding in multivariable analysis. Esophageal varices were the only independent predictor for major bleeding (OR 17.4). Among MPN-SVT, risk of subsequent vascular events was skewed towards venous thromboses compared to controls. However, MPN-SVT clinical course was overall benign: SVT were enriched in PMF with lower IPSS, resulting in significantly longer survival than controls; survival was not affected in PV and slightly reduced in ET. MPN-U with SVT (n = 55) showed a particularly indolent phenotype, with no signs of disease evolution. In the to-date largest, contemporary cohort of MPN-SVT, VKA were confirmed effective in preventing recurrence, unlike cytoreduction, and safe; the major risk factor for bleeding was esophageal varices that therefore represent a major therapeutic target.

Second cancer in Philadelphia negative myeloproliferative neoplasms (MPN-K). A nested case-control study.

We conducted a large international nested case-control study including 1881 patients with Philadelphia-negative myeloproliferative neoplasms (MPN). Cases (n = 647) were patients with second cancer (SC: carcinoma, non-melanoma skin cancer, hematological second cancer, and melanoma) and controls (n = 1234) were patients without SC, matched with cases for sex, age at MPN diagnosis, date of MPN diagnosis, and MPN disease duration. The aim was to evaluate the risk of SC after exposure to cytoreductive drugs. Patients exposed to hydroxyurea (HU) (median: 3 years) had a risk of SC similar to unexposed patients (OR = 1.06, 95% CI 0.82-1.38). In contrast, in cancer-specific stratified multivariable analysis, HU had two-fold higher risk of non-melanoma (NM) skin cancer (OR = 2.28, 95% CI 1.15-4.51). A significantly higher risk of NM-skin cancer was also documented for pipobroman (OR = 3.74, 95% CI 1.00-14.01), ruxolitinib (OR = 3.87, 95% CI 1.18-12.75), and for drug combination (OR = 3.47, 95% CI 1.55-7.75). These three drugs did not show excess risk of carcinoma and hematological second cancer compared with unexposed patients. Exposure to interferon, busulfan, and anagrelide did not increase the risk. In summary, while it is reassuring that no excess of carcinoma was documented, a careful dermatologic active surveillance before and during the course of treatments is recommended.

Phase II Study of Sequential Infusion of Donor Lymphocyte Infusion and Cytokine-Induced Killer Cells for Patients Relapsed after Allogeneic Hematopoietic Stem Cell Transplantation.

Seventy-four patients who relapsed after allogeneic stem cell transplantation were enrolled in a phase IIA study and treated with the sequential infusion of donor lymphocyte infusion (DLI) followed by cytokine-induced killer (CIK) cells. Seventy-three patients were available for the intention to treat analysis. At least 1 infusion of CIK cells was given to 59 patients, whereas 43 patients received the complete cell therapy planned (58%). Overall, 12 patients (16%) developed acute graft-versus-host disease (aGVHD) of grades I to II in 7 cases and grades III to IV in 5). In 8 of 12 cases, aGVHD developed during DLI treatment, leading to interruption of the cellular program in 3 patients, whereas in the remaining 5 cases aGVHD was controlled by steroids treatment, thus allowing the subsequent planned administration of CIK cells. Chronic GVHD (cGVHD) was observed in 11 patients (15%). A complete response was observed in 19 (26%), partial response in 3 (4%), stable disease in 8 (11%), early death in 2 (3%), and disease progression in 41 (56%). At 1 and 3 years, rates of progression-free survival were 31% and 29%, whereas rates of overall survival were 51% and 40%, respectively. By multivariate analysis, the type of relapse, the presence of cGVHD, and a short (<6 months) time from allogeneic hematopoietic stem cell transplantation to relapse were the significant predictors of survival. In conclusion, a low incidence of GVHD is observed after the sequential administration of DLI and CIK cells, and disease control can be achieved mostly after a cytogenetic or molecular relapse.

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.

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.

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.

Randomized Trial Comparing R-CHOP Versus High-Dose Sequential Chemotherapy in High-Risk Patients With Diffuse Large B-Cell Lymphomas.

Purpose The benefit of high-dose chemotherapy with autologous stem-cell transplantation (ASCT) as first-line treatment in patients with diffuse large B-cell lymphomas is still a matter of debate. To address this point, we designed a randomized phase III trial to compare rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP)-14 (eight cycles) with rituximab plus high-dose sequential chemotherapy (R-HDS) with ASCT. Patients and Methods From June 2005 to June 2011, 246 high-risk patients with a high-intermediate (56%) or high (44%) International Prognostic Index score were randomly assigned to the R-CHOP or R-HDS arm, and 235 were analyzed by intent to treat. The primary efficacy end point of the study was 3-year event-free survival, and results were analyzed on an intent-to-treat basis. Results Clinical response (complete response, 78% v 76%; partial response, 5% v 9%) and failures (no response, 15% v 11%; and early treatment-related mortality, 2% v 3%) were similar after R-CHOP versus R-HDS, respectively. After a median follow-up of 5 years, the 3-year event-free survival was 62% versus 65% ( P = .83). At 3 years, compared with the R-CHOP arm, the R-HDS arm had better disease-free survival (79% v 91%, respectively; P = .034), but this subsequently vanished because of late-occurring treatment-related deaths. No difference was detected in terms of progression-free survival (65% v 75%, respectively; P = .12), or overall survival (74% v 77%, respectively; P = .64). Significantly higher hematologic toxicity ( P < .001) and more infectious complications ( P < .001) were observed in the R-HDS arm. Conclusion In this study, front-line intensive R-HDS chemotherapy with ASCT did not improve the outcome of high-risk patients with diffuse large B-cell lymphomas.

Primary treatment response rather than front line stem cell transplantation is crucial for long term outcome of peripheral T-cell lymphomas.

Outcome of systemic peripheral T-cell lymphomas (PTCL) is unsatisfactory and no controlled clinical study guides the therapy. Phase II studies suggest to consolidate response achieved after front-line treatment with stem cell transplant (SCT). We retrospectively evaluate the impact of front-line SCT consolidation in a single Center cohort of 209 patients treated during the last two decades. Median age was 49 years (range 15-85) with a prevalence of male sex (61%), advanced stage (68%) while IPI was >2 in 44%. Primary treatment was MACOP-B (39%) CHO(E)P (39%), intensive regimens (18%) or others (4%). Complete response to primary treatment (i.e. before SCT) was 60% (5% partial remission). Forty-four patients further proceeded to SCT while 92 did not receive consolidation. Outcome of primary responders was good, with a 3-year overall survival of 74% (82% in ALCL ALK+ and 69% for the other histologies). By multivariate analysis a better overall survival was significantly associated with IPI<2 (P=0.001), primary response (P=0.000), and ALCL ALK+ (P=0.012). The multivariate analysis performed on responders, showed that only IPI was predictive of a better survival while ALCL ALK+ and undergoing SCT were not. Response to primary treatment rather than post-remission programs is the crucial determinant of PTCL outcome.

Rate of primary refractory disease in B and T-cell non-Hodgkin's lymphoma: correlation with long-term survival.

BACKGROUND: Primary refractory disease is a main challenge in the management of non-Hodgkin's Lymphoma (NHL). This survey was performed to define the rate of refractory disease to first-line therapy in B and T-cell NHL subtypes and the long-term survival of primary refractory compared to primary responsive patients. METHODS: Medical records were reviewed of 3,106 patients who had undergone primary treatment for NHL between 1982 and 2012, at the Hematology Centers of Torino and Bergamo, Italy. Primary treatment included CHOP or CHOP-like regimens (63.2%), intensive therapy with autograft (16.9%), or other therapies (19.9%). Among B-cell NHL, 1,356 (47.8%) received first-line chemotherapy with rituximab. Refractory disease was defined as stable/progressive disease, or transient response with disease progression within six months. RESULTS: Overall, 690 (22.2%) patients showed primary refractory disease, with a higher incidence amongst T-cell compared to B-cell NHL (41.9% vs. 20.5%, respectively, p<0.001). Several other clinico-pathological factors at presentation were variably associated with refractory disease, including histological aggressive disease, unfavorable clinical presentation, Bone Marrow involvement, low lymphocyte/monocyte ration and male gender. Amongst B-cell NHL, the addition of rituximab was associated with a marked reduction of refractory disease (13.6% vs. 26.7% for non-supplemented chemotherapy, p<0.001). Overall, primary responsive patients had a median survival of 19.8 years, compared to 1.3 yr. for refractory patients. A prolonged survival was consistently observed in all primary responsive patients regardless of the histology. The long life expectancy of primary responsive patients was documented in both series managed before and after 2.000. Response to first line therapy resulted by far the most predictive factor for long-term outcome (HR for primary refractory disease: 16.52, p<0.001). CONCLUSION: Chemosensitivity to primary treatment is crucial for the long-term survival in NHL. This supports the necessity of studies aimed to early identify refractory disease and to develop different treatment strategies for responsive and refractory patients.

The lymphocyte to monocyte ratio improves the IPI-risk definition of diffuse large B-cell lymphoma when rituximab is added to chemotherapy.

The peripheral blood lymphocyte to monocyte ratio (LMR) at diagnosis can be clinically relevant in patients with diffuse large B-cell lymphoma (DLBCL). We reviewed the outcome of 1,057 DLBCL patients followed from 1984 to 2012 at four centers. LMR was analyzed as a clinical biomarker by receiver-operating characteristic (ROC) analysis and Harrell's C-statistics. Patients were characterized by a median age of 61 years, International Prognostic Index (IPI) score of >2 in 39%, and were treated with a rituximab-containing chemotherapy in 66%. LMR proved strongly predictive for survival in patients treated with rituximab-based programs, but not in those receiving chemotherapy alone. Additionally, an LMR value of ≤2.6 (as determined by ROC analysis) was associated with a worst performance status, a higher lactate dehydrogenase (LDH) level, an advanced clinical stage, and a higher IPI score (P = 0.000). In patients treated with rituximab-supplemented chemotherapy programs, an LMR value of <2.6 was found in most of the primary refractory patients (75%) which proved as the best cutoff to predict both response and survival (P = 0.018). Finally, multivariate analysis and Harrell's C-statistics confirmed the IPI-independent role of LMR on survival (P = 0.0000). In conclusion, LMR is a potent predictor of clinical response and survival in DLBCL treated with rituximab-containing chemotherapy.

High cure rates in Burkitt lymphoma and leukemia: a Northern Italy Leukemia Group study of the German short intensive rituximab-chemotherapy program.

We evaluate the long-term results of a prospective clinical study enrolling more than 100 adult patients with Burkitt lymphoma/leukemia. Depending on extent of disease, treatment consisted of six to eight rituximab infusions and four to six courses of intensive chemotherapy (attenuated in patients aged >55 years) with high-dose methotrexate, fractionated ifosfamide/cyclophosphamide, other drugs in rotation, and intrathecal chemoprophylaxis. One-hundred five patients were treated (median age 47 years, range 17-78 years); 48% had Burkitt leukemia, 25% were older than 60 years, 37% had an Eastern Cooperative Oncology Group performance score >1, and 14% were positive for human immunodeficiency virus. The complete response rate and 3-year overall and disease-free survival rates were 79%, 67% and 75%, respectively, ranging from 100% to 45% for survival (P=0.000) and from 100% to 60% for disease-free survival (P=0.01) in patients with low, intermediate and high adapted International Prognostic Index scores. In multivariate analysis, only age (≤ versus >60 years) and performance status (0-1 versus >1) retained prognostic significance, identifying three risk groups with overall and disease-free survival probabilities of 88% and 87.5%, 57% and 70.5%, 20% and 28.5% (P=0.0000 and P=0.0001), respectively. The relapse rate was only 7% in patients treated with an intercycle interval ≤ 25 days. This regimen achieved 100% curability in patients with low adapted International Prognostic Index scores (21% of total), and very close to 90% in patients aged ≤ 60 years with performance score 0-1 (48% of total). Rapid diagnosis of Burkitt lymphoma/leukemia with prompt referral of patients to prevent clinical deterioration, and careful supervision of treatment without chemotherapy delay can achieve outstanding therapeutic results. ClinicalTrials.gov ID, NCT01290120.

Hydroxyurea in essential thrombocythemia: rate and clinical relevance of responses by European LeukemiaNet criteria.

A definition of response by cytoreductive therapy in essential thrombocythemia was recently provided by the European LeukemiaNet (ELN). Complete, partial, or no clinicohematologic responses were defined on the bases of platelet count, disease-related symptoms, spleen size, and white blood cell count. To provide estimates and clinical correlation of responses according to these criteria, we retrospectively examined 416 essential thrombocythemia patients treated with hydroxyurea for at least 12 months. Complete response, partial response, and no response were 25%, 58%, and 17%, respectively. Age more than 60 years and JAK2V617F mutation were significant predictors of response. After a median follow-up of 3.9 years, we registered 23 deaths, 16 hematologic transformations, and 27 thrombotic events (rate, 1.66% patients/year). Age, previous thrombosis, leukocytosis (white blood cell count > 10 x 10(9)/L), but not ELN responses, were independently associated with higher risk of thrombosis. The actuarial probability of thrombosis was significantly influenced by leukocytosis (P = .017) and not by platelet count, indicating that platelet number does not seem of prime relevance in the definition of ELN response.

A short low-dose imatinib trial allows rapid identification of responsive patients in hypereosinophilic syndromes.

Although imatinib may be effective in hypereosinophilic syndromes, the exact response kinetics are not known. Imatinib was administered at 100-400 mg/d each week in a 12-week response-oriented schedule, targeting a complete clinical and haematological remission (CR). CR was achieved in 11/23 patients (6/6 with FIP1L1-PDGRFA rearrangement and 5/17 without, P = 0.006), most after 2 weeks of 100 mg/d imatinib. The maximum imatinib dose had no effect in early unresponsive patients. Low-dose, short-course imatinib may represent a rational choice for identifying responsive cases, both within and outside the pre-defined FIP1L1 rearrangement subset.

JAK2V617F allele burden and thrombosis: a direct comparison in essential thrombocythemia and polycythemia vera.

OBJECTIVE: A direct comparison of the incidence and risk factors of major thrombosis in essential thrombocythemia (ET) and polycythemia vera (PV) according to their respective JAK2V617F allele burden is the object of this study. MATERIALS AND METHODS: We compared the rate (%/patients/year) of major thrombosis in 867 ET patients (57% JAK2V617F) with that of 415 PV patients (all JAK2V617F) and examined risk factors. RESULTS: Patients with ET wild-type, ET V617F, and PV showed a rate of thrombosis of 1.4%, 2.1%, and 2.7%/patients/year, respectively. The latter was found to progressively increase according to time of diagnosis. Actuarial probability of arterial and venous thrombosis in the first 5 years of diagnosis was roughly similar in the three groups. While in the subsequent periods, the curves of mutated ET patients diverged from wild-type, and after 10 to 15 years the ET-mutated arm approached PV. CONCLUSION: These findings support the concept of a continuum between ET JAK2 mutated and PV, not only in reference to the hematological phenotype, but also in terms of vascular events.

Identification of patients with poorer survival in primary myelofibrosis based on the burden of JAK2V617F mutated allele.

A total of 186 patients with primary myelofibrosis (PMF) were genotyped for JAK2V617F at diagnosis aimed at analyzing the correlation of mutational status and mutated allele burden with outcome variables, including time to anemia, leukocytosis, leukopenia, thrombocytopenia, massive splenomegaly, leukemia, and with overall survival. A total of 127 JAK2V617F-mutated patients (68% of whole series) were divided in quartiles of V617F allele burden. After a median follow-up of 17.2 months, 23 patients died, 15 because of leukemia. A JAK2V617F mutated status did not impact on the rate of leukemia transformation or overall survival. Patients in the lower quartile had shorter time to anemia and leukopenia and did not progress to large splenomegaly. Furthermore, survival was significantly reduced in the lower quartile compared with upper quartiles and JAK2 wild-type patients. In multivariate analysis, factors associated with reduced survival were age, a blast count more than 1%, and a JAK2V617F burden within first quartile. Causes of death in the lower quartile were represented mainly by systemic infections. We conclude that a low JAK2V617F allele burden at diagnosis is preferentially associated with a myelodepletive rather than myeloproliferative phenotype and represents an independent factor associated with shortened survival in patients with PMF.

Thrombocytosis and leukocytosis interaction in vascular complications of essential thrombocythemia.

To elucidate the role of thrombocytosis, alone or in combination with standard (age, previous cardiovascular events) and novel (leukocytosis, JAK2(V617F) mutational status) risk factors, in the cardiovascular events of essential thrombocythemia (ET), we analyzed a cohort of 1063 patients. We found that a platelet count at diagnosis greater than 1000 x 10(9)/L was associated with significantly lower rate of thrombosis in multivariable analysis and, if combined with leukocytes less than 11 x 10(9)/L, pointed to a "low-risk" category with a rate of thrombosis of 1.59% of patients/year. On the contrary, the highest risk category (thrombosis rate, 2.95% of patients/year) was constituted of patients with leukocytosis, lower platelet count, and a JAK2(V617F) mutated genotype in most cases (77% vs 26% in the low-risk group), independently from standard risk factors. These data challenge the theory that elevated platelet count increases thrombosis risk in ET and suggest prospective clinical trials to support this hypothesis.

Characteristics and clinical correlates of MPL 515W>L/K mutation in essential thrombocythemia.

Among 994 patients with essential thrombocythemia (ET) who were genotyped for the MPLW515L/K mutation, 30 patients carrying the mutation were identified (3.0%), 8 of whom also displayed the JAK2V671F mutation. MPLW515L/K patients presented lower hemoglobin levels and higher platelet counts than did wild type (wt) MPL; these differences were highly significant compared with MPLwt/JAK2V617F-positive patients. Reduced hemoglobin and increased platelet levels were preferentially associated with the W515L and W515K alleles, respectively. MPL mutation was a significant risk factor for microvessel disturbances, suggesting platelet hyperreactivity associated with constitutively active MPL; arterial thromboses were increased only in comparison to MPLwt/JAK2wt patients. MPLW515L/K patients presented reduced total and erythroid bone marrow cellularity, whereas the numbers of megakaryocytes, megakaryocytic clusters, and small-sized megakaryocytes were all significantly increased. These data indicate that MPLW515L/K mutations do not define a distinct phenotype in ET, although some differences depended on the JAK2V617F mutational status of the counterpart.