Perspectives on thrombosis in essential thrombocythemia and polycythemia vera: is leukocytosis a causative factor?

• Published in: Blood Vol. 114; no. 4; pp. 759 - 763
• Main Authors: Barbui, Tiziano, Carobbio, Alessandra, Rambaldi, Alessandro, Finazzi, Guido
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 23.07.2009; Americain Society of Hematology; American Society of Hematology
• Series: Perspective
• Subjects: Aged; Aged, 80 and over; Biological and medical sciences; Cohort Studies; Disease Susceptibility; Diseases of red blood cells; Follow-Up Studies; Hematologic and hematopoietic diseases; Humans; Leukemias. Malignant lymphomas. Malignant reticulosis. Myelofibrosis; Leukocyte Count; Leukocytosis - complications; Medical sciences; Middle Aged; Platelet Count; Polycythemia Vera - complications; Polycythemias; Risk Factors; Sensitivity and Specificity; Thrombocythemia, Essential - complications; Thrombosis - etiology; Vascular disease; Myeloproliferative syndrome; Essential thrombocythemia; Leukocytosis; Hematology; Cardiovascular disease; Polycythemia vera; Malignant hemopathy; Thrombosis; Cancer
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2009-02-206797

Leukocyte (WBC) count has been recently identified as an independent predictor of major thrombosis in both essential thrombocythemia (ET) and polycythemia vera (PV). However, whether leukocytosis should be simply considered a marker for vascular disease or whether elevated WBC levels actually contribute directly to causing such disorders is presently matter of many studies. By adopting epidemiologic criteria for causation, we have examined the characteristics to support this association such as (1) strength, (2) consistency, (3) specificity, (4) temporality, (5) biologic gradient, (6) plausibility, (7) experimental evidence, and (8) analogy. Our conclusion supports the notion that baseline leukocytosis in ET and PV patients adds prognostic significance to existing risk factors and that may be considered causative of vascular events. These developments could induce clinicians to incorporate WBC count into standard clinical practice. However, we need prospective clinical studies with stratification of patients according to their baseline leukocyte counts. Until such evidence is available, the decision on how to manage these patients should continue to follow conventional criteria.