Disease characteristics and clinical outcome in young adults with essential thrombocythemia versus early/prefibrotic primary myelofibrosis.

In the present study, we investigated disease characteristics and clinical outcome in young patients (< 40 years) with World Health Organization (WHO)-defined essential thrombocythemia (ET) compared with early/prefibrotic primary myelofibrosis (PMF) with presenting thrombocythemia. We recruited 213 young patients (median age, 33.6 years), including 178 patients (84%) with WHO-defined ET and 35 patients (16%) showing early PMF. Median follow-up time was 7.5 years. A trend for more overall thrombotic complications, particularly arterial, was seen in early PMF compared with ET. Progression to overt myelofibrosis was 3% in ET and 9% in early PMF, but no transformation into acute leukemia was observed. Combining all adverse events (thrombosis, bleeding, and myelofibrosis), the rate was significantly different (1.29% vs 3.43% of patients/year, P = .01) in WHO-ET and early PMF, respectively. In multivariate analysis, early PMF and the JAK2V617F mutation emerged as independent factors predicting cumulative adverse events.