ABSTRACT
The term “myelodysplastic syndromes” (MDS) covers a wide range of het erogeneous clonal disorders of hematopoiesis that are characterized by re fractory cytopenias and morphological abnormalities of the bone marrow and peripheral blood, and that have been called preleukemia, preleukemic syn dromes, oligoblastic leukemia, smoldering leukemia, and subacute leukemia [70]. At least two and generally all three hematopoietic cell lineages are in volved mostly with cytopenia [14], while bone marrow cellularity is usually increased [30]. According to the definition of the French-American-British (FAB) group, patients with less than 5% blast cells in the bone marrow are classified as refractory anemia (RA) or RA with ring sideroblasts (RARS), patients with 5% to 20% blast cells in the marrow as RA with excess of blasts (RAEB), and patients with 21 % to 30% bone marrow blasts as RAEB in trans formation (RAEB-T) [14] (Table 1). Patients with chronic myelomonocytic leukemia (CMML) have a significant proportion of monocytes in the circula tion (> 1000/pL), and up to 20% blast cells in the marrow. Depending on the initial blast cell load, 10% to 40% of these patients will proceed to acute myeloid leukemia (AML). In addition, infections due to neutropenia and thrombocytopenic bleeding are frequent causes of death [50,70].
