Chronic Myelomonocytic Leukemia



Chronic Myelomonocytic Leukemia


David Czuchlewski, MD









The peripheral blood in chronic myelomonocytic leukemia shows, by definition, a monocytosis > 1 × 109/L. In this 71-year-old man, mature monocytes are predominant. Note the dysplastic neutrophil image.






The bone marrow in chronic myelomonocytic leukemia is usually hypercellular with a “chaotic” proliferation of both granulocytic and monocytic lineages, often apparent at low power.


TERMINOLOGY


Definitions



  • Chronic myelomonocytic leukemia (CMML) is a myelodysplastic/myeloproliferative neoplasm



    • Like other entities in this “overlap” category, it combines features of both myelodysplastic syndrome and myeloproliferative neoplasia


  • Specific diagnostic criteria for CMML (WHO 2008)



    • Persistent peripheral blood monocytosis > 1 × 109/L


    • No Philadelphia chromosome or BCR-ABL1 fusion gene


    • No rearrangement of PDGFRA or PDGFRB



      • These should be specifically excluded in cases with eosinophilia


    • < 20% blasts in blood and bone marrow



      • Blasts in this case include myeloblasts and blast equivalents (monoblasts and promonocytes)


    • Dysplasia in 1 or more myeloid lineages



      • If dysplasia is absent or minimal, CMML may still be diagnosed if clonal cytogenetic or molecular abnormality is present or if monocytosis has persisted for at least 3 months and other causes of monocytosis are excluded


  • CMML may be further subcategorized based on blast percentage (including equivalents)



    • CMML-1



      • < 5% in peripheral blood and < 10% in bone marrow


    • CMML-2



      • Between 5-19% in peripheral blood or 10-19% in bone marrow


      • CMML-2 is also diagnosed when Auer rods are identified, regardless of blast percentage


ETIOLOGY/PATHOGENESIS


Heterogeneity of CMML



  • Cases range from those with predominant myelodysplastic features to those with more myeloproliferative findings


  • Given this heterogeneity, it is not surprising that pathognomonic genetic abnormalities have not been identified


  • Cytogenetic abnormalities are detected in up to 40% of cases, but none are specific for CMML



    • Common changes include



      • Trisomy 8


      • Monosomy 7/del(7q)


      • Abnormalities of 12p


  • RAS mutations are identified in up to 40% of cases



    • Other frequently mutated genes include TET2, CBL, and RUNX1


  • JAK2 V617F mutations have been reported in some cases, but this change is neither strongly associated with nor characteristic of CMML

Jun 13, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Chronic Myelomonocytic Leukemia
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