What is the prevalence of unclassifiable myelodysplastic syndromes (MDS-U)?

Updated: Jul 21, 2020
  • Author: Robert P Hasserjian, MD; Chief Editor: Christine G Roth, MD  more...
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The incidence of unclassifiable myelodysplastic syndromes (MDS-U) is unknown; however, the incidence appears to represent only a small fraction of myelodysplastic syndrome (MDS) cases. In one case series, MDS-U, as defined by the 2008 World Health Organization (WHO) classification criteria, comprised only 3% of MDS cases lacking excess bone marrow blasts. [5]

This figure represented a much smaller proportion of cases than when the 2001 WHO classification criteria [6] were applied to the same cohort of cases, reflecting the more specific definition of MDS-U) in the 2008 versus the 2001 classification systems, as well as the broadening of the definition of certain other MDS entities. [5, 7] The relatively low proportion of MDS-U cases in the newer 2008 classification validates its use in assigning the vast majority of MDS cases to specific diagnostic groups with relatively defined biologic features and clinical behavior.

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