Canterbury DHB

Introduction

Classification of myeloid neoplasms (MNs) according to the 2016 WHO classification scheme:

1. Myeloproliferative neoplasms (MPNs):
   • Chronic myeloid leukemia, BCR-ABL1-positive (CML)
   • Chronic neutrophilic leukaemia (CNL)
   • Polycythaemia vera (PV)
   • Essential thrombocythaemia (ET)
   • Primary myelofibrosis (PMF)
   • Chronic eosinophilic leukemia, not otherwise specified (CEL-NOS)
   • MPN, unclassifiable
2. Myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, and FGFR1
3. Myelodysplastic syndrome (MDS)/MPN
4. MDS
5. Acute myeloid leukemia (AML)

The revised 2016 WHO Classification of Myeloid Neoplasms makes several changes to the 2008 classification:

• The term myeloproliferative neoplasm reflects evidence that these are clonal disorders. They are characterised by proliferation of one or more of the myeloid cell lines.
• Most, if not all, MPNs result from abnormalities in genes which encode tyrosine kinases or regulators of these pathways leading to constitutive activation and proliferation.
• It emphasises that all key information available, including morphology, immunophenotype, molecular and cytogenetic findings and clinical features, should be incorporated into the diagnosis – referred to as the "integrated approach" to disease definition.
• Bone marrow biopsy remains important, but it notes problems with inter-observer variability in morphologic determination (especially ET vs early PMF and PV) and the need for a standardised approach to diagnosis.
• It highlights the importance of genetic/molecular markers, in particular JAK2V617F (and exon 12 mutations), calreticulin (CALR) and myeloproliferative leukemia (MPL) mutations in MPN, but notes that the absence of mutations does not exclude an MPN and that these mutations may be seen in other myleoid neoplasms, such as MDS or AML.
• It expands the category for myeloid/lymphoid neoplasms with eosinophilia and gene arrangements.
• Mastocytosis has been removed from the MPN subgroup and is now considered a separate entity.

This section reviews the MPNs, as detailed in the 2016 WHO classification of tumours of haematopoietic and lymphoid tissues¹ (see Chapter 2).

Topic Code: 6210