Introduction

Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell disorders which are distinguished by cytopenias in the face of hypercellular marrows and dysplastic hematopoietic cell lines. Up into the 1970s MDS have been called “preleukemia” expressing the proximity of MDS to acute myeloid leukemia (AML), and their capacity to evolve into AML over time. Although MDS is the currently accepted term, the pathophysiology of MDS varies widely extending from abnormalities of apoptosis and differentiation to proliferation and maturation arrest. It is nowadays also better understood that there are notable differences between MDS and AML, a separation which is also underlined by the clinical manifestations and prognosis of MDS, which are primarily determined by cytopenias and not leukemic transformation. The complexity of pathophysiology and resultant heterogeneity of prognosis have led to several recent attempts to fine tune criteria for diagnosis and classification. In addition, recent years have also seen important advances of treatment with respect to hematopoietic growth factors, iron chelation, and particularly epigenetic therapy and immunomodulatory inhibitory derivatives (e.g., lenalidomide). These developments have made the care of patients with MDS more demanding but at the same time more satisfying as the possibilities for patients with MDS are now larger than before.