Refractory anemia with excess of blasts in transformation: analysis of reclassification according to the WHO proposals.

The category of "refractory anemia with excess blasts in transformation" (RAEB-T) has been abandoned in the new WHO-classification of myelodysplastic syndromes (MDS). The majority of patients previously belonging to this category are now classified as acute myeloid leukaemia (AML). In the FAB-classification, patients had been assigned to the RAEB-T category if they had either (1) a medullary blast count between 20 and 30% or (2) a peripheral blast count of at least 5%, or (3) Auer rods detectable, irrespective of the blast count. We analyzed these subtypes of RAEB-T in terms of hematological characteristics, karyotype anomalies, and prognosis. Patients with more than 20% medullary blasts and patients with at least 5% peripheral blasts as the sole defining parameter for RAEB-T had a median survival of 6 months, as compared to 11 months in patients with Auer rods as the sole defining parameter. The presence of Auer rods therefore does not convey a particularly bad prognosis and does not justify placing patients in a high-risk category of MDS or even classifying them as AML. This finding supports the elimination of Auer rods as a parameter for classification in the new WHO system. On the other hand, the reclassification into RAEB II (according to WHO proposals) of previous RAEB-T patients with a peripheral blast count of at least 5% is problematic, because this feature predicts a median survival not different from that of AML patients.