title: Leukocytosis and risk stratification assessment in essential thrombocythemia.
abstract: OBJECTIVE
  Established risk factors for thrombosis in essential thrombocythemia (ET) include age and previous vascular events. We aimed to refine this risk stratification by adding baseline leukocytosis.
  
  
  METHODS
  We enrolled 657 patients with ET followed for a median of 4.5 years who developed 72 major thrombosis. Cox proportional hazard model was performed to analyze the thrombotic risk and to discriminate ET patients with or without thrombosis, multivariable C statistic index was used. We searched for leukocytes cutoff with the best sensitivity and specificity by a receiver operating characteristic curve.
  
  
  RESULTS
  Results confirmed that age and prior events are independent risk factors for thrombosis and showed a gradient between baseline leukocytosis and thrombosis. On the contrary, no significant association was found either for JAK2(V617F) allele burden and for other laboratory parameters, including platelet number. In the model with conventional risk factors alone, C statistic ratio for total thrombosis was 0.63 and when leukocytosis was added, the change was small (C = 0.67). In contrast, in younger and asymptomatic patients (low-risk category), C statistic value indicated an high risk for thrombosis in patients with leukocytosis, similar to that calculated in conventionally defined high-risk group (C = 0.65). The best leukocyte cutoff values for predicting the events was found to be 9.4 (x 10(9)/L).
  
  
  CONCLUSIONS
  We suggest to include baseline leukocytosis in the risk stratification of ET patients enrolled in clinical trials.
authors.affiliation: Hematology Department, Ospedali Riuniti di Bergamo, Bergamo, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Carobbio
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Antonioli
authors.forename: Paola
authors.initials: P
authors.lastname: Guglielmelli
authors.forename: Alessandro M
authors.initials: AM
authors.lastname: Vannucchi
authors.forename: Federica
authors.initials: F
authors.lastname: Delaini
authors.forename: Vittoria
authors.initials: V
authors.lastname: Guerini
authors.forename: Guido
authors.initials: G
authors.lastname: Finazzi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rambaldi
authors.forename: Tiziano
authors.initials: T
authors.lastname: Barbui
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood; D002648:Child; D005260:Female; D005838:Genotype; D006801:Humans; D053614:Janus Kinase 2 / Q000145:classification / Q000235:genetics*; D007964:Leukocytosis / Q000150:complications* / Q000201:enzymology / Q000235:genetics; D008297:Male; D008875:Middle Aged; D011087:Polycythemia Vera / Q000503:physiopathology; D011379:Prognosis; D016016:Proportional Hazards Models; D012307:Risk Factors; D013920:Thrombocythemia, Essential / Q000150:complications*; D013927:Thrombosis / Q000209:etiology*
chemical_list: D053614:Janus Kinase 2