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

This study investigates disease characteristics and clinical outcome in young patients (<40 years) with WHO-defined essential thrombocythemia (ET) in comparison to early/prefibrotic primary myelofibrosis (PMF) with presenting thrombocythemia. We recruited 213 young patients (median age 33.6 years) including 178 patients (84%) consistent with WHO-defined ET and 35 patients (16%) showing early PMF. Median follow-up was 7.5 years. A trend for more overall thrombotic, particularly arterial, complications was seen in early PMF compared to ET. Progression to overt myelofibrosis was 3% in ET and 9% in early PMF, but no transformation into acute leukemia was observed. By combining all adverse events (thrombosis, bleeding, myelofibrosis) the rate was significantly different (1.29 vs. 3.43% patients/year, p=0.01) in WHO-ET and early PMF, respectively. In multivariate analysis early PMF and JAK2V617F mutation emerged as independent factors in predicting cumulative adverse events.