[Classification and clinical findings of myelodysplastic syndromes]

Myelodysplastic syndromes (MDS) are a group of related disorders in which bone marrow stem cells malfunction, while the type is diagnosed based on the WHO classification revised in 2008. Although the diagnosis largely depends on the cytomorphology, it is difficult to diagnose MDS based on the morphology alone, particularly in patients with < 5% blasts in the bone marrow and a normal karyotype. In Japan, a grading system for the diagnostic accuracy of MDS was proposed in 2007, and evaluation of dysplasia (high, intermediate, low, minimal) is a characteristic part. Morphologic dysplastic changes are classified into highly specific category A (pseudo-Pelger-Huet anomaly, degranulation of neutrophils, micro-megakaryocytes, ringed sideroblasts) and less specific category B (dysplasia other than category A). With the use of this grading system, diagnostic problems should be reduced. Flow cytometry has also been proposed as a tool to improve the evaluation of marrow dysplasia, because immunophenotyping is an accurate method for quantitative and qualitative evaluations of hematopoietic cells, and MDS specimens have been found to exhibit abnormal expressions of several cellular antigens. In addition, the molecular classification of MDS has received marked attention in recent years. New molecular markers including RPS14, TET2, IDH1/2, SF3B1, ASXL1, RUNX1, TP53, EZH2, JAK2, and WT1 have been revealed to be important for the prognosis, as well as diagnosis and classification. In this report, we review MDS diagnostic approaches from the viewpoints of cytomorphology, immunophenotyping, and cytogenetics.