Dysplastic erythroid precursors in the myelodysplastic syndromes and the acute myeloid leukemias: Is there biologic significance? (How should blasts be counted?)

• In a series of MDS patients 15.7% of cases have 50% or more erythroid precursors (EP).
• Some have used the 50% rule for classifying blasts to move cases to a higher grade MDS.
• The “50%” rule does not enhance the prognostic impact of the classifications on survival or time to transformation.".
• This method of classification is no longer recommended.

The role of bone marrow dysplastic erythroid precursors (EP) in both MDS and AML has been the subject of considerable debate over the past several decades.We have analyzed a large series of adults with MDS and focused on whether any% of EP identified in the bone marrow aspirates of over 1400 patients selected from the Dusseldorf, Germany adult MDS Registry has prognostic relevance. The data was examined for varying% of blasts, the WHO prognostic MDS subtypes and the IPSS-R.We did not identify any adjustment of bone marrow blast percentage by%EP, incuding the 50% rule” developed by the FAB leukemia working group, to have a meaningful impact on outcome, either leukemic risk of progression or overall survival. There was a trend for a%EP<15% to actually have a worse survival than any other EP subset.We can no longer recommend the application of the “50% rule” in the calculation of the% of myeloblasts in bone marrow aspirates.