The revised who classification of myeloproliferative neoplasms – What has changed?

Abstract

The group of Philadelphia-negative myeloproliferative neoplasms (MPNs) includes polycythemia vera (PV), primary myelofibrosis (PMF) and essential thrombocythemia (ET), which are clonal haematopoietic stem cell disorders characterised by proliferation of one or more myeloid cell lineages. The 2016 revised WHO classification of has introduced following changes and/or recommendations for the diagnostic pathway and criteria in these diseases with respect to the previous 2008 edition. (1) Identification of the new entity ‘prefibrotic/early PMF’ (on the basis of bone marrow morphology and distinguishable from ET) presenting with a higher tendency to develop overt myelofibrosis or acute leukaemia and characterised by inferior survival. (2) Central role of bone marrow morphology of megakaryocytes in the differential diagnosis among typical in ET, and atypical in both PMF forms. (3) A new distinction of reticulin fibrosis grade in PMF: grade 1 in prefibrotic/early PMF and grade 2-3 in PMF. (4) The threshold the HB level as diagnostic criteria in PV is lowered to 16.5 g/dL for men and 16 g/dL for women. (5) The inclusion of all mutually exclusive MPN driver mutations (JAK2, CALR, and MPL) as major diagnostic criteria in ET and PMF; 10–15% of these patients are triple negative, and in these cases the search for an additional clonal marker (e.g., mutations in ASXL1, EZH2, TET2, IDH1/IDH2, SRSF2, and SF3B1) is warranted.