Myelodysplastic syndromes (MDS) are a heterogeneous group of acquired clonal disorders in which the underlying lesion is a clonal abnormality in the development of hematopoietic stem and progenitor cells (dysplasia), leading to ineffective hematopoiesis and an increased risk of malignant transformation. It is characterized by an increased or normal number of hematopoietic cells of all lineages in the bone marrow, but morphological changes that look like obvious developmental abnormalities, and a significant decrease of blood cells of all lineages in the peripheral blood. The risk of developing acute myeloid leukemia (AML) is very high.