Hematopoietic progenitor and stem cells are believed to lie dormant within the adult bone marrow microenvironment in a state characterized by both mitotic and metabolic quiescence. This state of cell-cycle quiescence has been the focus or target of many studies aimed at identifying cells with such mitotic properties for their eventual isolation and characterization. On the other hand, knowledge of the type, frequency, and primitive status of dividing cells in patients with malignant hematopoietic diseases is very important for the hematologist designing therapies aimed at targeting cycling cancer cells with cell-cycle-specific chemotherapuetic drugs that can spare noncycling normal hematopoietic stem cells (HSC).
