Proposed changes in the definitions of acute myeloid leukemia and myelodysplastic syndrome: are they helpful?

For most of the 20th century, subclassification of acute myeloid leukemia (AML) was based on the resemblance of blasts to normal hematopoiesis. This approach was standardized by the French-American-British (FAB) group. Because of limited clinical relevance, clinicians resorted to other patient characteristics to determine treatment and predict outcome in AML. A different approach based on the relationship of a case to myelodysplastic syndrome (MDS) has been proposed. The new World Health Organization (WHO) subclassification of AML includes elements of this new proposal but retains as a major category the historical subclassification. The WHO group has also proposed modifications of the FAB subclassification of MDS. These MDS proposals have generated discussion of diagnostic criteria for MDS and a philosophical discussion of whether MDS should still be considered a syndrome, or rather a specific set of diseases characterized by genetic instability and poor outcome.