The cancer stem cell (CSC) hypothesis suggests that clonogenic growth potential within an individual tumor is restricted to a specific and phenotypically defined cell population. Evidence for CSC in human tumors initially arose from studies of AML, but functionally similar cell populations have been identified in an increasing number of malignancies. Despite these findings, controversy surrounds the CSC hypothesis, especially the generalization that clonogenic tumor cells are rare. Nevertheless, efforts to define the cellular processes regulating self-renewal and resistance to anticancer therapeutics, two of the major properties ascribed to CSC, are likely to provide useful insights into tumor biology as a whole. BMT has been at the forefront of clinically translating basic stem cell concepts starting with the original hypothesis that normal hematopoietic precursors could rescue patients from myeloablative doses of radiation or chemotherapy. Even today, a better understanding of CSC may enhance ongoing efforts to induce specific and effective anti-tumor immune responses in both the allogeneic and autologous setting. It is also likely that new clinical research approaches will be required to accurately evaluate novel CSC-targeting strategies. Owing to the capacity to produce remissions in most diseases, SCT may provide the ideal clinical platform to carry out these investigations by studying the ability of anti-CSC agents to prolong relapse free and overall survival.
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