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. (Blood. 2008;112:844-847)

Few investigators have evaluated the usefulness of the JAK2 V617F mutation for explaining the phenotypic variations and for predicting the risk of major clinical events in primary myelofibrosis (PMF). In a transversal survey we assayed by allelespecific polymerase chain reaction (PCR) the JAK2 V617F mutational status in 304 patients with PMF. Multiple DNA samples were collected prospectively from 64 patients, and a highly sensitive quantitative PCR was used as a confirmatory test. In a longitudinal prospective study we determined the progression rate to clinically relevant outcomes in 174 patients who had JAK2 mutation determined at diagnosis. JAK2 V617F was identified in 63.4% of patients. None of the V617F-negative patients who were sequentially genotyped progressed to become V617F positive, whereas progression rate from heterozygous to homozygous mutation was 10 per 100 patient-years. JAK2 V617F mutation contributed to hemoglobin, aquagenic pruritus, and platelet count variability, whereas homozygous mutation was independently associated with higher white blood cell count, larger spleen size, and greater need for cytoreductive therapies. Adjusting for conventional risk factors, V617F mutation independently predicted the evolution toward large splenomegaly, need of splenectomy, and leukemic transformation. We conclude that JAK2 V617F genotype should be considered in any future risk stratification of patients with PMF. (Blood. 2007;110: [4030][4031][4032][4033][4034][4035][4036]

We genotyped 370 subjects with primary myelofibrosis (PMF) and 148 with postpolycythemia vera/postessential thrombocythemia (PPV/PET) MF for mutations of EZH2. Mutational status at diagnosis was correlated with hematologic parameters, clinical manifestations, and outcome. A total of 25 different EZH2 mutations were detected in 5.9% of PMF, 1.2% of PPV-MF, and 9.4% of PET-MF patients; most were exonic heterozygous missense changes. EZH2 mutation coexisted with JAK2V617F or ASXL1 mutation in 12 of 29 (41.4%) and 6 of 27 (22.2%) evaluated patients; TET2 and CBL mutations were found in 2 and 1 patients, respectively. EZH2-mutated PMF patients had significantly higher leukocyte counts, blast-cell counts, and larger spleens at diagnosis, and most of them (52.6%) were in the high-risk International Prognostic Score System (IPSS) category. After a median follow-up of 39 months, 128 patients (25.9%) died, 81 (63.3%) because of leukemia. Leukemia-free survival (LFS) and overall survival (OS) were significantly reduced in EZH2-mutated PMF patients (P ‫؍‬ .028 and P < .001, respectively); no such impact was seen for PPV/ PET-MF patients, possibly due to the low number of mutated cases. In multivariate analysis, survival of PMF patients was predicted by IPSS high-risk category, a < 25% JAK2V617F allele burden, and EZH2 mutation status. We conclude that EZH2 mutations are independently associated with shorter survival in patients with PMF. (Blood. 2011;118(19):5227-5234) IntroductionThe identification of the JAK2V617F mutation 1-4 represented a seminal discovery in the field of Philadelphia-chromosomenegative chronic myeloproliferative neoplasms (MPNs), 5 providing clues to the pathogenesis, 6 prompting a revision of the diagnostic criteria, 7 and culminating in the development of clinical trials with JAK2 (and JAK1) inhibitors. 8,9 The JAK2V617F mutation occurs in almost all patients with polycythemia vera (PV) and in 50%-70% of those with essential thrombocythemia (ET) and primary myelofibrosis (PMF). Soon after the identification of the JAK2V617F mutation, mutations in JAK2 exon 12 were described in rare patients with JAK2V617F-negative PV and mutations in MPL were reported in 5%-10% of ET or PMF subjects. The complexity of the molecular pathogenesis of MPNs is reinforced by discovery of additional mutations in TET2, 10 ASXL1, 11 CBL, 12 IDH1/IDH2, 13 and IKZF1. 14 These mutations are detected in a minority of patients at different phases of the disorder, including leukemic transformation, and are variably associated each other and with JAK2 or MPL mutations.We recently identified novel loss-of-function mutations in EZH2 in 1 of 30 (3%) PV and in 4 of 30 PMF patients (13%), as well as in 11%-25% of patients with myelodysplastic syndromes (MDS) and in 10% of patients with MDS/MPN. 15 Mutations were spread throughout the gene and included missense, nonsense, and premature stop codons; both monoallelic and biallelic mutations were described. Among patients with MDS/MPN, survival was significantly worse in those with EZH2 muta...

SummaryThe clinical and haematological phenotype of patients with myelofibrosis harbouring MPL W515L/K mutation has not been thoroughly investigated. Of 217 myelofibrosis subjects, 18 (8AE2%) had an MPL mutation, four of which (22%) , were more frequently female, were older (61 years vs. 57 years; P ¼ 0AE02), presented with more severe anaemia (haemoglobin, 101 g/l vs. 121 g/l; P ¼ 0AE002) and were more likely to require regular transfusional support (P ¼ 0AE012). These data indicate that MPL mutation in myelofibrosis characterises patients with more severe anaemic phenotype.

Increased microvessel density contributes to abnormal BM and spleen microenvironment in myelofibrosis (MF). Taking advantage of the JAK2V617F mutation as a marker of malignancy, in the present study, we investigated whether splenic endothelial cells (ECs) obtained from capillaries by laser microdissection or from fresh spleen tissue by cell culture or cell sorting harbored such mutation in patients bearing the mutation in their granulocytes and undergoing splenectomy for therapeutical reasons. To extend the analysis to the ECs of large vessels, endothelial tissue from the splenic vein was also studied. We found JAK2V617F+ ECs in 12 of 18 patients also bearing the mutation in their granulocytes. In 3 patients, the mutation was found in at least 2 different EC samples obtained by laser microdissection, cell culture, or cell sorting. The mutation was detected in the splenic vein ECs of 1 of 6 patients investigated. In conclusion, we provide evidence that some ECs from the spleen and splenic veins of patients with MF bear the JAK2V617F mutation. We suggest that splenic ECs are involved in the process of malignant transformation in MF.