ABSTRACT
Myelodysplastic syndromes (MDS) (1) and acute myeloid leukemia (AML) (2) usually manifest in cellular bone marrow as a proliferation of abnormal clones. The clones of MDS, although abnormal, are capable of differentiation whereas the AML clones are characterized by an increased amount of blast cells* owing to maturation arrest. Rather than a proliferation of clones, abnormal clones in hypocellular or hypoplastic bone marrow has been reported in about 8-20% of MDS cases (4-8) and 7.7-15% of AML cases (9-14). MDS cases with hypocellular bone marrow (hypo-MDS) can be difficult to distinguish from aplastic anemia (AA) whereas AML cases with hypocellular bone marrow (hypo-AML) can be difficult to distinguish from refractory anemia with excess blasts (RAEB). Whether these minor subgroups of MDS or AML cases are distinct clinical entities has been a matter of long debate.
