The myelodysplastic syndromes (MDS) are 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 increased risk of developing acute myeloid leukemia.
MDS fall 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 in spite of the hyper-cellular bone marrow. The causes that contribute to the MDS are not well understood, but some may be caused by cytotoxic agents, chemicals, alkylating agents, radiation, or chemotherapeutic drugs. Exposure to environmental agents may have similar effects on the bone marrow stem cells (eg, exposure to benzene, cigarette, agricultural chemicals, or industrial solvents). Some hereditary factors, such as Fanconi anemia, can be associated with increased risk of developing MDS.
The syndromes occur predominantly in adults with median age of 70. MDS are rare in children, and are more predominant 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 certain subtypes of MDS, such as in MDS with excess blasts.