Hematopoietic Abnormalities in Patients With Cancer.

Hematopoiesis is the process of blood cell production, which involves the maintenance and proliferation of hematopoietic progenitor cells and their differentiation into mature, functional erythrocytes, leukocytes, and platelets. Normal hematopoiesis depends on the presence of (1) normal pluripotent hematopoietic stem cells, which are capable of maintaining differentiated hematopoietic cell production throughout an individual’s lifetime, (2) a bone marrow microenvironment that is supportive of stem cell survival and proliferation and of differentiation of stem cells to committed hematopoietic progenitor cells and mature hematopoietic cells, and (3) a complex system of highly regulated hematopoietic growth factors with overlapping lineage specificities, which are crucial in regulating the proliferation, differentiation, and survival of hematopoietic cells. The central feature of pluripotent hematopoietic stem cells is that they are capable of both self-renewal and irreversible differentiation into mature hematopoietic cells. Although the duration of survival and the function of individual stem cells are controversial, the stem cell pool as a whole has, on average, an approximately equal chance of self-replication or differentiation, thus assuring continuing hematopoietic cell production throughout the life of the individual. Although single stem cells and their direct repopulated progeny may survive for long periods of time, there may be a dynamic process by which some stem cells cease functioning and are replaced by other stem cells that previously had been resting for a prolonged period of time in the G0 phase of the cell cycle. 1 Regardless of the situation, the purpose of the stem cells is accomplished, and normal individuals have stem cells that maintain hemopoiesis at a stable level throughout their lifetimes, yet retain the ability to respond relatively promptly to stress situations in which marked increases in one or all lineages of mature hematopoietic cells are required.