[Myeloproliferative neoplasms: revisions in the 2016 WHO criteria]

The 2016 revised WHO classification of tumors of hematopoietic and lymphoid tissues has incorporated novel molecular markers, such as calreticulin (CALR) mutations, for the diagnosis of myeloproliferative neoplasms (MPNs). Typically, CALR mutations are detected in 25%-30% of patients with essential thrombocythemia (ET) or primary myelofibrosis (PMF) and can lead to frameshifts that produce proteins with a novel C-terminal. In addition, the CALR mutation plays a crucial role in the MPN pathogenesis. The second major revision comprises the change in RBC parameters for polycythemia diagnosis; additionally, it emphasizes BM biopsy for the diagnosis of PV. Previously, PV was often underdiagnosed when considering the Hb levels of >18.5 g/dl for males and >16.5 g/dl for females; thus, the 2016 revision lowered these levels to >16.5 g/dl for males and >16.0 g/l for females. The third major revision is the introduction of a novel entity "prefibrotic/early" PMF (prePMF) to PMF. Although megakaryocytic proliferation and atypia were observed in in BM biopsy specimens of prePMF, these were not accompanied by reticulin fibrosis > grade 1. Thus, the inferior prognosis of prePMF was reported in comparison with "true" ET.