Leukocytosis at Diagnosis in Patients with Essential Thrombocythemia Is a Risk Factor for Transformation into Myelofibrosis

Myelofibrosis (MF) represents the major long-term complication of essential thrombocythemia (ET). There is evidence that leukocytosis at diagnosis is associated with poorer survival in patients with ET. In this study, we retrospectively evaluated 143 patients with ET, diagnosed in agreement with WHO criteria, followed in a single centre over >10 years. Nine of them transformed into MF (post-essential thrombocythemia-myelofibrosis PET-MF). We compared PET-MF data at diagnosis with that of the remaining 134 patients (ET-1) and with a selected sub-group of ET-1 (ET-2, 19 pats) sex, age and follow-up duration matched to PET-MF. The PET-MF evolution rate was 4.6 per 1000 person-years; white blood cells count (WBC) count, haemoglobin levels and hematocrit were higher in PET-MF than in ET-1 (P = 0.01) while only WBC was higher than in ET-2 (P = 0.01). With multivariate analysis, only WBC count retained its signifi-cance. Our study highlights the prognostic relevance of leukocytosis on myelofibrotic transformation of ET.