[Preleukemic disorders]

Certain hematopoietic disorders and immunodeficiency states are known to carry a risk of developing acute nonlymphocytic leukemia. In the past some of them have been classified by a variety of terms ranging from refractory anemia to preleukemia, but are currently grouped into a new concept of the myelodysplastic syndromes (MDS). The purpose of this article is to briefly review the updated knowledge of the MDS with emphasis on the clonal origin, natural history and mechanisms of leukemogenesis.