Comparison of Clinical and Molecular Features between Patients with Essential Thrombocythemia and Early/Prefibrotic Primary Myelofibrosis Presenting with Thrombocytosis in Taiwan

Objectives: The clinical presentations of essential thrombocythemia (ET) may be quite similar to early/prefibrotic primary myelofibrosis (pre-PMF), especially in pre-PMF presenting with thrombocytosis (pre–PMF-T), but may be associated with a different outcome. It is very important to distinguish these two entities. The aim of this study was to address the clinical and prognostic relevance of distinguishing pre–PMF-T from ET. Methods: All patients, including 258 with ET and 105 with pre–PMF-T, received JAK2^V617F, MPL (exon 10), and CALR (exon 9) mutation analysis and allele burden measurement for JAK2^V617F and CALR mutants. Results: Patients with pre–PMF-T had an older age and higher leukocyte and platelet counts but lower hemoglobin levels than patients with ET. Patients with pre–PMF-T had a shorter overall, leukemia-free, and thrombosis-free survival compared with patients with ET. Patients with ET had a higher rate of cerebral ischemic stroke, whereas patients with pre–PMF-T tended to have splanchnic vein thrombosis. The frequencies of JAK2^V617F, CALR, and MPL mutations and CALR allele burden were no different, but JAK2^V617F allele burden was significantly higher in pre–PMF-T. Patients with pre–PMF-T with the JAK2^V617F mutation had an inferior overall survival and thrombosis-free survival, whereas the status of driver gene mutations did not influence the outcomes of patients with ET. Conclusions: ET and pre–PMF-T were two distinct disease entities and exhibited different clinical phenotype, genotype, and outcomes.