Diagnosis, classification, and course of myelodysplastic syndromes. The myelodysplastic syndromes are bone marrow stem cell disorders that result in disorderly and ineffective hematopoiesis. They are prognostically heterogenous. Approximately one third of cases evolve to acute myeloid leukemia. Many additional cases terminate in severe bone marrow failure. The French-American-British Working Group classification of the myelodysplastic syndromes defines morphologic and prognostic groups. Cytogenetic and in vitro cell culture characteristics are important prognostic indicators. 