Myelodysplastic syndrome (MDS) is not a single disease, but rather a group of disorders affecting the bone marrow. Therefore, no single approach is likely to be of universal benefit to all patients. In fact, one way to consider the complexity of MDS is to think of it as being to the bone marrow what pneumonia is to the lungsā€”the response of an organ to a variety of assaults, such as aging, toxic exposure, infections, and autoimmunity. Among infections of the lungs alone, pneumonia could be the result of a variety of possible pathogens, including bacteria, viruses, tuberculous, or fungal agents. Similarly, MDS is the response of the bone marrow to a variety of unknown insults and cannot be treated as a single disease. Until recently, there was no approved treatment for MDS, but as of May 2004, 5-azacytidine (a methyltransferase inhibitor) has been approved by the Food and Drug Administration (FDA) in the United States for use in all subtypes of MDS. Most patients who will then fall in the category of relapsed or refractory disease will include those who have received some sort of supportive care (SC) in the form of transfusions or growth factors, and most likely, a trial of 5-azacytidine. Subsequent treatment options would depend upon the type of MDS and general condition of this predominantly elderly group of patients. For those with high-risk disease, the danger comes from a rapid transformation toward acute leukemia, while for those with low-risk disease, it is the deepening profundity of cytopenias, which pose a potentially lethal threat of bleeding or infection. This chapter will outline the new types of treatments that have emerged to treat these patients and summarize some of the clinical responses already seen in preliminary clinical trials.

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