Evolution of classification of the myelodysplastic syndromes, from the era when these syndromes were poorly characterized and collectively known as “preleukemia” (the prevailing term in the 1960s and early 1970s for what is now known as MDS), through the 1976/1982 FAB classifications and, in the last decade, the two WHO systems.
 FAB indicates French-American-British Co-operative Group; WHO, World Health Organization; MDS, myelodysplastic syndromes; RA, refractory anemia; RARS, refractory anemia with ring sideroblasts; CMML, chronic myelomonocytic leukemia; RAEB, refractory anemia with excess blasts; RAEB-t, refractory anemia with excess blasts in transformation; RN, refractory neutropenia; RT, refractory thrombocytopenia; RCMD, refractory cytopenias with multilineage dysplasia; RCMD-RS, refractory cytopenias with multilineage dysplasia and ring sideroblasts; MDS-U, MDS unclassifiable; RCC, refractory cytopenias of childhood; RCUD, refractory cytopenias with unilineage dysplasia; MDS/MPD, myelodysplastic/myeloproliferative diseases.