Myelodysplastic syndromes, from French-American-British to World Health Organization: comparison of classifications on 431 unselected patients from asingle institution

In 1999 a working group of the World Health Organization (WHO) published a revised classification for myelodysplastic syndromes (MDS): RA, RARS, refra ctory cytopenia with multilineage dysplasia (RC+Dys), RAES I and II, del (5 q) syndrome, and MDS unclassifiable. Chronic myelomonocytic leukemia (CMML) and RAEB-t were excluded. Standard French-American-British (FAB) and new W HO classifications have been compared in a series of patients (n = 431) fro m a single center, analyzing morphologic, clinical, and cytogenetic data. A ccording to the WHO findings, dysgranulocytopoiesis or dysmegakaryocytopoie sis only were found in 26% of patients with less than 5% medullary blasts. These patients are thus unclassified and should remain in the subgroups RA and RARS. Splitting of heterogeneous RAEB into 2 subgroups according to bla st count was supported by a trend to a statistically significant difference in the single-center study population. Patients with CMML whose white bloo d cell counts are above 13 000/muL may be excluded from the MDS classificat ion, as warranted by WHO, but a redistribution of patients with dysplastic CMML according to medullary blast count leads to more heterogeneity in othe r WHO subgroups. Although the natural courses of RAEB-T and acute myeloid l eukemia (AML) with dysplasia are different, comparable median survival dura tions after treatment in patients with RAEB-T and AML were in favor of the proposed 20% medullary blast threshold for AML. The homogeneity of subgroup s was studied by evaluating prognostic scores. A significant shift into low er IPSS risk groups was evident in the new classification. These data canno t provide evidence for the new WHO proposal, which should not be adopted fo r routine clinical use at present. Some of its aspects can provide a starti ng point for further studies involving refined cytogenetics and clinical re sults. (C) 2001 by The American Society of Hematology.