Stem cells are vital throughout life because they can develop into specialized tissue. Recently, however, scientists have discovered that damaged or altered stem cells may be the driving force behind some kinds of cancer when their specialization takes a malignant turn for the worse.

Stem cells were first identified in leukemia in 1997. Since then, they have been found in breast cancer and certain brain tumors, including glioblastoma multiforme, the most aggressive brain malignancy in adults. Although it was widely thought that most cells in a tumor could cause it to grow, researchers now believe that in some cancers, a small population of stem cells gives rise to all the other cells. When tumor cells are transplanted into experimental mice, only the stem cell variety spurs new cancer growth.

Neural stem cells normally develop into neurons, glia and other cell types. Stem cells found in brain tumors are similar but have genetic mutations that lead to uncontrolled growth. Harley Kornblum, director of the Neural Stem Cell Research Center at the University of California, Los Angeles, is searching for drugs that might inhibit or kill tumor stem cells. Because there are many kinds of brain cancer, Kornblum cautions that they must be approached individually. “We don’t think there’s a one-size-fits-all” mechanism, he says, pointing out that one type of brain tumor called medulloblastoma is caused by “external granule” cells.

Nevertheless, because stem cells activate their genes differently than other cells do, doctors may be able to use genetic analysis to assign more effective treatment to certain patients. Scientists are now focusing on methods to block the unique pathways by which cancer stem cells regenerate, because it seems clear that the stem cells must be eradicated to stop tumor growth. If they succeed, less destructive chemotherapy or radiation, or other treatments, may be possible.