Organ Systems, Bone Marrow, WHO Classification, MDS

Myelodysplastic Syndrome, Unclassifiable – (MDS-U)

2016 revision subdivides category into three entities

  • with 1% blood blasts
  • with single lineage dyaplasia (SLD) and pancytopenia
  • based on defining cytogenetic abnormality
Diagnostic Criteria – with 1% PB blasts
  • Multiple lineages (1-3) with dysplasia (>10% for each affected lineage)
  • 1-3 cytopenias
  • +/- ring sideroblasts
  • <5% bone marrow blasts
  • 1% peripheral blood blasts
  • No Auer Rods
  • Any cytogenetic abnormalities
Diagnostic Criteria – with SLD and pancytopenia
  • Single lineage with dysplasia (>10% for affected lineage)
  • 3 cytopenias
  • +/- ring sideroblasts
  • <5% bone marrow blasts
  • <1% peripheral blood blasts
  • No Auer Rods
  • Any cytogenetic abnormalities
Diagnostic Criteria – with defining cytogenetic abnormality
Immunohistochemistry
The use of immunohistochemistry (IHC) in many of the MDS syndromes is limited.  Identifying an increased blast population is one of the most useful, and may indicate a more aggressive course or transformation to acute myelogenous leukemia (AML).  Helpful IHC markers may include:
 
Stain
Comment
CD34 marks immature cells including myeloblasts.  In the setting of AML, it is ~70% sensitive.  A subset of lymphoblasts may express CD34.
CD117 is a specific myeloid marker, and marks a subset of myeloblasts.  The expression is dim, and one often must look at 20-40X to clearly see expression.  Mast cells (fried egg looking cell) will have very strong expression.
CD71 marks nucleated erythroid cells.  This may be helpful in quantitating and differentiating erythroid cells from myeloid cells.  This marker may be set-up as a double stain with CD34.
In the setting of hematopoietic cells, E-Cadherin marks immature erythroid cells.  Like CD71, E-Cadherin may be useful to differentiate immature erythroid cells from immature myeloid cells.
TdT is a sensitive lymphoblast (~95%) marker.  It is not entirely specific for lymphoblasts, but other markers can help clarify diagnostic difficulties (B and T-cell markers).  
References
Swerdlow SH, Campo E, Harris, NL, Jaffe ES, Pileri SA, Stein H, Thiele J (Eds):  WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (Revised 4th edition). IARC: Lyon 2017
 
Hematopathology. [edited by] Jaffe, ES. 1st. ed. Elsevier, Inc. © 2011.