Studies on erythropoiesis in the myelodysplastic syndrome

A variety of primary hematologic disorders were described, all characterised by ineffective hematopoiesis, peripheral blood cytopenias, and hypercellular bone marrow (Bjorkman, 1956, Rheingold et aJ., 1963, Linman et aJ., 1978). Lack of uniform definitions for these disorders, often referred to as smoldering leukemia, preleukemia or refractory anemia, resulted in both difficulties in classification and problems in predicting disease outcome. In an effort to resolve these problems, in 1982 the French-AmericanBritish (F AB) Cooperative Study group proposed a new classification system for these bone marrow disorders and termed them myelodysplastic syndromes (MDS)(Bennett et aJ., 1982). Based on cellular morphology and on the number of blast cells in the peripheral blood and bone marrow, five subtypes of MDS were defined: Refractory anemia (RA), refractory anemia with ring sideroblasts (RARS) , refractory anemia with excess blasts (RAEB), refractory anemia with excess blasts in transformation (RAEB-t), and chronic myelomonocytic leukemia (CMML).