Essential thrombocythemia vs. early/prefibrotic myelofibrosis: why does it matter.

Essential thrombocythemia (ET) and primary myelofibrosis (PMF), together with polycythemia vera (PV) are Phildelphia-negative (Ph-neg) classical myeloproliferative neoplasms (MPN). ET has been traditionally identified by thrombocytosis and absence of relevant bone marrow (BM) fibrosis, while PMF by BM reticulin or collagen fibrosis with megakaryocyte hyperplasia and dysplasia, and extramedullary hematopoiesis. These diagnostic profiles have been challenged since 2001 when the World Health Organization (WHO) has included in the domain of PMF a new category of patients, namely early/prefibrotic MF, characterized by the absence of relevant reticulin fibrosis in BM, dual megakaryocyte and granulocyte proliferation, and megakaryocyte dysplasia. This review is focused on summarizing the diagnostic uncertainties of early/prefibrotic myelofibrosis, recent advances in our understanding of the biology of the variant, and the accompanying translational implications.