Mutations and long-term outcome of 217 young patients with essential thrombocythemia or early primary myelofibrosis

We investigated the influence of molecular status on disease characteristics and clinical outcome in young patients (⩽40 years) with World Health Organization (WHO)-defined essential thrombocythemia (ET) or early/prefibrotic primary myelofibrosis (early-PMF). Overall, 217 patients with ET (number 197) and early-PMF (number 20) were included in the analysis. Median follow-up time was 10.2 years. The cumulative incidence of thrombosis, hemorrhages and disease evolution into myelofibrosis/acute leukemia were 16.6%, 8.6% and 3% at 15 years, respectively. No differences were detectable between ET and early-PMF patients, although the latter cohort showed a trend for worse combined-event free survival (EFS). Mutation frequency were 61% for JAK2 V617F, 25% for CALR and 1% for MPL W515K, and were comparable across WHO diagnosis; however, JAK2 V617F allele burden was higher in the early-PMF group. Compared with JAK2 V617F-positive patients, CALR -mutated patients displayed higher platelet count and lower hemoglobin level. CALR mutations significantly correlated with lower thrombotic risk (9.1% versus 21.7%, P =0.04), longer survival (100% versus 96%, P =0.05) and better combined-EFS (86% versus 71%, P =0.02). However, non-type 1/type 2 CALR mutations (‘minor’ mutations) and abnormal karyotype were found to correlate with increased risk of disease evolution. At last contact, six patients had died; in five cases, the causes of death were related to the hematological disease and occurred at a median age of 64 years (range: 53–68 years). Twenty-eight patients (13%) were unmutated for JAK2 , CALR and MPL : no event was registered in these ‘triple-negative’ patients.