Abstract

Stem cell biology has come of age. Unequivocal proof that stem cells exist in the haematopoietic system has given way to the prospective isolation of several tissue-specific stem and progenitor cells, the initial delineation of their properties and expressed genetic programmes, and the beginnings of their utility in regenerative medicine. Perhaps the most important and useful property of stem cells is that of self-renewal. Through this property, striking parallels can be found between stem cells and cancer cells: tumours may often originate from the transformation of normal stem cells, similar signalling pathways may regulate self-renewal in stem cells and cancer cells, and cancer cells may include 'cancer stem cells' — rare cells with indefinite potential for self-renewal that drive tumorigenesis.

1. Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Palo Alto, California 94305, USA
2. Howard Hughes Medical Institute, and Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109-0934, USA
3. Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109-0936, USA
4. Present address: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
5. These authors contributed equally to this work

Correspondence to: Irving L. Weissman¹ (e-mail: Email: irv@stanford.edu).