Myelodysplastic syndromes (MDS) are a group of clonal hematopoietic stem cell neoplasms characterized by peripheral blood cytopenia (due to ineffective hematopoiesis and apoptosis of cells earlier than normal), dysplasia in one or more myeloid cell lines, and an increased risk of developing acute myeloid leukemia.
MDS falls into two main categories: de novo cases with no previous exposure to cytotoxic agents and secondary cases related to prior chemotherapy or radiation therapy.
The clonal disorders of MDS lead to ineffective hematopoiesis despite the hyper-cellular bone marrow. The causes that contribute to MDS are poorly understood, but cytotoxic agents, chemicals, alkylating agents, radiation, or chemotherapeutic drugs may cause some. Environmental agents may have similar effects on bone marrow stem cells (e.g., exposure to benzene, cigarettes, agricultural chemicals, or industrial solvents). Some hereditary factors, such as Fanconi anemia, can increase the risk of developing MDS.
The syndromes occur predominantly in adults with a median age of 70. MDS is rare in children and more prevalent in males than females. Many of the features seen in adult MDS are also observed in childhood MDS. These include morphologic, immunophenotypic, and genetic abnormalities.
Progression to acute myeloid leukemia is the natural course of MDS. The risk of developing AML is higher in specific subtypes of MDS, such as in MDS with excess blasts.
