Myeloproliferative Neoplasm, Unclassifiable



Myeloproliferative Neoplasm, Unclassifiable


Kaaren K. Reichard, MD





Key Facts


Terminology



  • Definition



    • Clonal hematopoietic neoplasm


    • Meets criteria for an MPN


    • Features are not sufficient to render more specific MPN diagnosis


Microscopic Pathology



  • Early phase of disease



    • Thrombocytosis


    • Mild neutrophilic leukocytosis


    • Blasts < 10%


    • BM hypercellular


    • Abnormal megakaryocytic proliferation


    • Minimal fibrosis


  • Late phase of disease



    • Leukoerythroblastosis


    • Increased blast %


    • Osteosclerosis


    • Marked fibrosis


Ancillary Tests



  • Immunophenotyping



    • CD34


  • Conventional cytogenetics



    • Exclude BCR-ABL1 fusion and rearrangements of PDFGRA, PDGFRB, and FGFR1


  • Molecular genetics



    • JAK2 V617F may be present; not specific


Top Differential Diagnoses



  • Specific MPN subtype


  • Reactive conditions


  • Underlying malignancy






PB smear shows moderate thrombocytosis and neutrophilic leukocytosis in a case of MPN-U. Criteria for a specific MPN subtype were not met.






Bone marrow core biopsy shows marked megakaryocytic proliferation image in a patient presenting with MPN-U. The bone is not osteosclerotic, and background hematopoiesis is evident image.


TERMINOLOGY


Abbreviations



  • Myeloproliferative neoplasm, unclassifiable (MPN-U)


Synonyms



  • Myeloproliferative disorder, unclassifiable


  • Myeloproliferative neoplasm, not otherwise specified


Definitions



  • Clonal hematopoietic neoplasm


  • Diagnostic criteria for MPN are met


  • Features are not sufficient to render more specific MPN diagnosis



    • Early disease presentation


    • End-stage disease precluding recognition of more specific underlying MPN


ETIOLOGY/PATHOGENESIS


Unknown



  • No definite etiology has been identified


Molecular Mutations



  • May be present (e.g., JAK2 V617F)


  • Likely pathogenetic to some extent


  • No specific mutations known so far


  • Confirms clonal disorder


CLINICAL ISSUES


Site



  • Peripheral blood (PB)


  • Bone marrow (BM)


  • Spleen


  • Liver


Presentation



  • Similar to other MPNs


  • Early disease



    • Variable cytoses


    • Unexplained deep-seated thrombotic events


    • No significant % blasts


  • Late-stage disease



    • Leukoerythroblastosis


    • Cytopenias


    • Marked hepatosplenomegaly


    • Increased blasts


    • Ultimate BM failure


Laboratory Tests



  • Complete blood cell count (CBC) with differential


  • PB and BM examination


  • Conventional cytogenetics


  • Exclude BCR-ABL1 fusion and rearrangements of PDGFRA, PDGFRB, and FGFR1


  • Molecular studies



    • JAK2 V617F mutation


Prognosis



  • Early disease



    • Specific MPN subtype may emerge


    • Outcome related to specific subtype


  • Late disease



    • Generally poor outcome


    • Bone marrow failure



      • Extensive BM fibrosis or increased blasts


    • Refractory splenomegaly


MICROSCOPIC PATHOLOGY


Typical Presentation of MPN-U



  • Early phase disease



    • Early or prodromal phase of essential thrombocythemia (ET), polycythemia vera (PV), or primary myelofibrosis (PMF)


    • Disease-defining features not yet present


    • JAK2 mutation may be present



  • Late-phase/advanced-stage disease



    • Marked myelofibrosis


    • Osteosclerosis


    • Increasing % blasts


Peripheral Blood Microscopic Features



  • Early phase of disease



    • Thrombocytosis


    • Mild neutrophilic leukocytosis


    • Blasts < 10%


    • Normal hemoglobin or mild anemia


  • Late phase of disease



    • Leukoerythroblastosis



      • Left shift in granulocytes


      • Variable % blasts


      • Teardrop-shaped red blood cells


      • Nucleated red blood cells


Bone Marrow Microscopic Features

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Jun 13, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Myeloproliferative Neoplasm, Unclassifiable

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