The New York Times reviews the state of research into cancer stem cells: "stem cells are the source of at least some, and perhaps all, cancers. At the heart of every tumor, some researchers believe, lie a handful of aberrant stem cells that maintain the malignant tissue. ... It's a very challenging population of cells to identify, but thus far in every cancer in which cells have been carefully screened they have been found ... If the notion of cancer stem cells is correct, how can they be eliminated without also killing the normal stem cells that are vital for maintaining the body's tissues? Researchers hope that the cancer stem cells, because of their excessive activity, may be more dependent than normal cells on certain cellular processes and thus will be more vulnerable to drugs that block those processes."