Bone marrow morphology and classification systems in myelodysplastic syndromes

SummaryOne of the hallmarks of myelodysplastic syndromes (MDS) is their morphological heterogeneity which complicates the diagnosis and classification of these bone marrow disorders. The French–American–British (FAB) classification system which is based on cytological findings and the blast cell percentage in the bone marrow (BM) and peripheral blood (PB) was the universally accepted reference standard for categorization of MDS samples from 1982 to 1999 when it was modified by an expert panel of the World Health Organization (WHO). The WHO classification system distinguishes eight subgroups of MDS and is based on three principles: distinction between unilineage and multilineage dysplasia of haematopoietic cells, definition of refined blast cell percentages in BM and PB for diagnosing patients with RAEB and AML, as well as incorporation of genetic data into the classification scheme. When compared to the FAB proposals, the WHO classification appears to define more homogeneous subgroups of patients and to provide greater prognostic power. However, prospective studies of large patient populations will be required to decide whether the WHO classification allows accurate risk assessment and facilitates clinical decision-making for individual MDS patients.