Spring 1997 Volume 4, Number 1 SUBTITLE Myelodysplastic Syndrome and Its Treatment - The term myelodysplastic syndrome (MDS) is used to describe a condition characterized by refractory cytopenias in patients whose bone marrows reveal dysplastic changes in at least two of the three hematopoietic cell lines. MDS often undergoes transformation into acute myeloid leukemia (AML), and the leukemias in these patients are generally less responsive to standard induction chemotherapy than those which arise de novo. Therefore, although the morphology of AML is similar regardless of whether the disease develops de novo or after transformation from MDS, the biology of the disease is not. Variations in marrow morphology and differing potentials for survival and transformation to AML among cases of MDS have led to the establishment of a morphologic classification scheme with five subgroups (see table on this page): refractory anemia (RA), refractory anemia with ringed sideroblasts (RARS), refractory anemia with excess blasts (RAEB), RAEB in transformation (RAEB-T), and chronic myelomonocytic leukemia (CMML). RA and RARS patients have fewer than 5% blasts in their bone marrow; RAEB patients have 5-20% blasts, and RAEB-T patients 20-30% blasts. Patients with AML have more than 30% blasts in their bone marrow. MDS can develop de novo (primary MDS) or can arise as a result of prior chemotherapy or chemoradiotherapy for other malignancies or as a result of exposure to a variety of marrow toxins (secondary MDS). Approximately 40-60% of patients with primary MDS have cytogenetic abnormalities at diagnosis, whereas more than 80% of patients with secondary MDS have abnormal karyotypes.
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