Stem cells: Good, bad and reformable

Viktor Janzen and David T. Scadden
Nature 441, 418-419 (25 May 2006) doi:10.1038/441418b; Published online 24 May 2006
Yilmaz et al. (page 475) and Zhang et al. (page 518)

The ability of stem cells to continuously supply vast numbers of cells is magnificent, but it can be devastating if it runs amok, as in some tumours. So what makes a normal stem cell turn bad, and can it be redeemed?

The stem cell is a bit like the griffin of mythology — half lion, half eagle; grand and powerful, but potentially monstrous in effect. These essentially unspecialized cells can renew their own population while supplying cells that mature (differentiate) into the specialized cells necessary for all tissues. Although this ability to reproduce and self-renew is sublime when functioning properly, its disorder creates masses of dysfunctional replicating cells. Indeed, stem-cell-like cells have been found in a range of human tumours. Not all cancer is due to a stem cell gone bad, but some cancer-initiating cells are probably stem cells, and the rest acquire the stem-cell feature of self-renewal. This raises the troubling spectre that normal stem cells and cancer stem cells might share the molecular features essential to their nature. So attempting to treat cancer by disrupting the functions of the cancer stem cells might also disturb normal stem cells — potentially fatally.