The FAB Collaborative Group classified MDS into five types according to the pathological hematopoietic characteristics, primitive cell ratio and monocyte count in peripheral blood and bone marrow of MDS patients: refractory anemia (RA), refractory anemia with ringed sideroblasts (RAS), refractory anemia with excess blasts in transformation (RAEB-t), refractory anemia with excess blasts in transformation (RAEB-t), and refractory anemia with excess blasts in transformation (RAEB-t). refractory anemia with excess blasts (RAEB), refractory anemia with excess blasts in transformation (RAEB-t), and chronic myelomonocytic leukemia (CMML).