Bone marrow neoplastic

Bone marrow - neoplastic myeloid

Myeloproliferative neoplasms (MPN)

WHO classification - MPN

Last author update: 1 August 2011
Last staff update: 24 March 2022

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PubMed Search: MPN WHO classification

Nikhil Sangle, M.D.
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Cite this page: Sangle N. WHO classification - MPN. website. Accessed April 2nd, 2023.
World Health Organization classification
WHO 2008 - Myeloproliferative neoplasms (MPN)
  • Chronic myelogenous leukemia
  • Polycythemia vera
  • Essential thrombocythemia
  • Primary myelofibrosis
  • Chronic neutrophilic leukemia
  • Chronic eosinophilic leukemia, not otherwise categorized
  • Mast cell disease
  • MPNs, unclassifiable

WHO 2001 - Chronic myeloproliferative diseases
  • Chronic myelogenous leukemia (Philadelphia chromosome, t(9;22)(q34;q11), BCR-ABL positive)
  • Chronic neutrophilic leukemia
  • Chronic eosinophilic leukemia (and the hypereosinophilic syndrome)
  • Polycythemia vera
  • Chronic idiopathic myelofibrosis (with extramedullary hematopoiesis)
  • Essential thrombocythemia
  • Chronic myeloproliferative disease, unclassifiable
Diagrams / tables

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Drawing of JAK2 mutation

Drawing of c-Mpl mutation

Clinical features
  • First described by William Dameshek in 1951 (Blood 1951;6:372)
  • WHO 2001: termed chronic myeloproliferative diseases
  • WHO 2008: termed myeloproliferative neoplasms, to emphasize the clonal evolution of these entities
  • All have effective clonal myeloproliferation with no dyserythropoiesis, no granulocyte dysplasia and no monocytosis; their phenotypic diversity is due to different mutations affecting tyrosine kinases or related molecules, causing different patterns of abnormal signal transduction
  • Initially hypercellular marrow with increased hematopoiesis, increased peripheral blood counts (often marked increase in all cell lines but with normal morphology) and extramedullary hematopoiesis in spleen with splenomegaly / other organomegaly; then spent phase with marrow fibrosis and cytopenia
  • CML frequently progresses to acute myelogenous leukemia (AML) but other myeloproliferative neoplasms only rarely progress to AML
  • There is considerable morphologic overlap among subtypes and with benign hyperplastic marrow conditions, requiring a multimodal diagnostic approach combining cytomorphology, cytogenetics and molecular methods for BCR-ABL negative cases (Ann Hematol 2008;87:1)
  • 4 color flow cytometry is helpful in diagnosis (Arch Pathol Lab Med 2003;127:1140)
  • Extramedullary hematopoiesis appears to be a clonal process (Hum Pathol 2007;38:1760) with JAK2 V617F mutation frequently present in splenic EMH cells (Mod Pathol 2007;20:929)
  • Occasionally has coexisting monoclonal B cell infiltrate in bone marrow detectable by IgH PCR but not by morphology (Mod Pathol 2004;17:1521)
  • May have nodal or extranodal tumor forming accumulations of plasmacytoid monocytes / interferon producing cells, which are clonal and related to underlying myeloid tumor (Am J Surg Pathol 2004;28:585)
  • Associated with chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension (Respiration 2008;76:295)
  • Usually prolonged survival
Microscopic (histologic) description
  • May have emperipolesis (ingestion of blood cells by megakaryocytes or other cells)
  • Rarely monocytic nodules similar to plasmacytoid monocyte nodules (Am J Clin Pathol 2003;120:874)
Molecular / cytogenetics description
  • JAK2 V617F mutation (Janus kinase 2 gene) present in most non CML chronic myeloproliferative diseases ( > 85% of polycythemia vera, 65% of essential thrombocythemia, 65% of chronic idiopathic myelofibrosis, Am J Surg Pathol 2007;31:233), causes constitutive tyrosine kinase activity
  • c-Mpl mutation (thrombopoietin receptor) occurs in essential thrombocythemia and idiopathic myelofibrosis (J Transl Med 2006;4:41)
  • FLT3 mutations are occasionally seen (Am J Clin Pathol 2006;126:530)
Additional references
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