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.