Validation of the WHO proposals for a new classification of primary myelodysplastic syndromes: a retrospective analysis of 1600 patients

In 1982, the French-American-British (FAB) cooperative group proposed a cla ssification of myelodysplastic syndromes (MDS) based on morphological featu res in blood and bone marrow, namely on medullary and peripheral blast coun t, Auer rods, ring sideroblasts and the number of monocytes in the peripher al blood. This classification has been used for numerous studies regarding morphology, prognosis and treatment of MDS. Some details of this morphologi cal classification remained unclear, and some patients were unclassifiable. A working group of the World Health Organization (WHO) recently proposed a new classification of MDS, based on a significant modification of the orig inal FAB proposals. CMML and RAEB-T were removed from the MDS classificatio n and RAEB was split into two groups with medullary blast counts below and above 10%. In addition, a group of patients with less than 5% medullary bla sts but evidence of multilineage dysplasia was defined. MDS patients with 5 q - as the sole chromosomal anomaly were also considered a separate group. The aim of the present study was to validate the new classification with re spect to prognostic importance, and to correlate it with cytogenetic and he matological features in a large series of patients (n = 1600) with a long-t erm follow up. We were able to confirm a significant difference in prognosi s between RAEB I and RAEB II, as well as a difference between refractory an emia and multilineage dysplasia. Furthermore, patients with 5q - anomaly ha d a much better prognosis than other WHO subtypes, but this was only true f or patients with a medullary blast count below 5%. In summary, the WHO clas sification appears to define morphological subgroups that are more homogene ous with respect to prognosis than the FAB subtypes. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.