Myelodysplastic syndromes versus acute myeloid leukaemia: biology or blasts—what truly defines the disease and does it matter?

The distinction between myelodysplastic syndromes and acute myeloid leukaemia remains a subject of debate, with direct implications for clinical decisions, trial eligibility, and allogeneic hematopoietic cell transplantation allocation. Although the historical 20% blast threshold in bone marrow is commonly used to separate myelodysplastic syndromes from acute myeloid leukaemia, emerging evidence shows that morphological, cytogenetic, and molecular features provide a more accurate framework for diagnosis and risk stratification.