The Stanford University Medical Center researchers said cancer stem cells are thought to be the ones that drive a cancer, and are therefore the targets of any cancer therapy that must kill them in order to be effective.

Understanding these cells has been a challenge, however, because they are rare, difficult to isolate and don't grow well in the lab, said Dr. Howard Chang, an assistant professor and senior author of the study.

"The upshot is that there may be a way to directly create cancer stem cells in the lab so you don't always have to purify these rare cells from patients in order to study them directly," said Chang.

He said the study also demonstrated that cancer stem cells are much more similar to the stem cells found in embryos, which can develop to form all tissue types, than they are to the more-restricted adult stem cells. That finding, said Chang, has important implications for understanding how cells go awry when they become cancerous.

The research appears in the journal Cell Stem Cell.