Several independent studies have provided strong evidence for the existence of cancer stem cells in some brain tumors, and potentially in skin and colon cancers as well. Like their powerful, healthy counterparts, the putative cancer stem cells have the ability to endlessly self-renew and produce progeny that can develop into all the different types of cells within a tumor. Some may even be resistant to many standard cancer therapies, and could be the cause of cancer relapse. But whether they actually exist in solid tumors is a controversial notion. Three studies published today won't end the debate, but they do lend greater credence to the theory, and could provide support for new approaches to cancer treatment.

Cancer stem cells are controversial partly because the experiments suggesting their existence have yielded inconsistent results. Experts say that could be due to the methods used to study them. Today's studies take advantage of imaging techniques that let researchers trace the fate of a cell and its progeny within a single mouse. All three groups looked at models of skin, brain, and colon cancer, and each study yielded varying degrees of support for cancer stem cells. The results suggest that at least some solid tumors carry the powerful cells, which may require special attention during cancer treatment.