Personalized management of essential thrombocythemia—application of recent evidence to clinical practice

The World Health Organization (WHO) classification system has recently strengthened the diagnostic criteria for essential thrombocythemia (ET) by lowering the threshold platelet count, underscoring its morphological distinction from early/prefibrotic myelofibrosis (MF) and incorporating molecular markers of clonality. The International Working Group for Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) examined the clinical relevance of this process in 1104 cases of locally diagnosed 'ET' and showed worse overall, leukemia-free and fibrosis-free survival, and a higher risk of bleeding in early/prefibrotic MF (n=180) vs WHO-defined ET (n=891). The risk of thrombosis was similar between the two entities and, in WHO-defined ET, was predicted by thrombosis history, older age, cardiovascular risk factors and JAK2V617F. A prognostic model based on these risk factors identified patient groups in ET with residual risk of thrombosis, despite treatment with conventional therapy. The main objectives of the current perspective are to underscore the prognostic importance of morphological confirmation in the diagnosis of ET and provide management recommendations, in both WHO-defined ET and early/prefibrotic MF, based on observations from the aforementioned IWG-MRT and other studies. In so doing, we are fully cognizant and sympathetic of the fact that some of our recommendations need to be tested in prospective controlled studies.