Beginning about 15 years ago, John Dick's team at the University of Toronto in Canada provided a new clue as to what makes cancer such a formidable foe. They found that only a tiny population of leukemia cells could transmit the cancer from one experimental animal to another. More remarkably, the cells had a property previously seen only in stem cells: the ability to produce an exact copy of themselves each time they divide, thereby maintaining the ability to reproduce in perpetuity. These socalled cancer stem cells, Dick suggested, might be what makes the disease so hard to eradicate with radiation or chemotherapy.rnSince then, such cells have been found in many other cancers, including those of the breast, brain, colon, and head and neck. "Cancer stem cells are being identified in virtually every cancer," says Max Wicha of the University of Michigan Comprehensive Cancer Center in Ann Arbor.
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