Cancers and normal tissue stem cells have much in common: Both have self-renewal capacity, and both develop into differentiated progeny. But do true cancer stem cells exist? We believe that they do and that this realization will have a major impact on the understanding and treatment of cancers. Putative cancer stem cells can be recognized by three attributes: They constitute a homogenous cell population; they, on their own, can initiate cancer; and they both self-renew and undergo differentiation into nontumorigenic progeny.
Many normal tissues start with stem cells. In a tightly regulated sequence, daughter cells undergo successive quantal steps in differentiation and have limited self-renewal capacity. This is an idea that has been around for a long time. For example, chromosome-marking experiments supporting the existence of stem cells for the hematopoietic system were published in 1967. Yet it took 20 years for the definitive demonstration of hematopoietic stem cells (HSC), ...
