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Abstract
Myelodysplastic syndrome (MDS) represents a heterogenous hematopoietic disorder derived from an abnormal multipotent progenitor cell. It is characterized by a hyperproliferative bone marrow, dysplasia of the cellular elements, and ineffective hematopoiesis. It is classified according to etiology into primary (de novo) MDS in which the etiology is still unclear, however, it is postulated to be related to occupational and environmental exposure to potentially genotoxic chemical. The other type is the secondary (therapy related) MDS which describes the development of MDS after known exposure to chemo/radiotherapy as part of the treatment for another diseases.
The pathogenesis of MDS is felt to be multifactorial, hematopoietic stem/progenitor cell abnormalities, immune dysregulation, abnormal marrow environment, and other factors are felt to contribute to this disease and its heterogeneity. It is generally accepted that apoptosis of marrow progenitors is the underlying cause of ineffective hematopoiesis and peripheral blood cytopenias in MDS.
The FAB classification divides MDS into five subgroups: refractory anemia (RA), refractory anemia with ringed siderolasts (RARS), refractory anemia with excess blasts (RAEB), RAEB in transformation (RAEB-t) and chronic myelomonocytic leukemia (CMML).