MOLECULAR BIOLOGY: Cancer's Perpetual Source?

The discovery of tumor cells that behave like stem cells suggests why cancer may be so hard to eradicate--and how new therapies might be targeted

Blood vessel stimulator. When transplanted into mouse brains, glioma stem cells form larger and more vascular tumors (middle row) than do nonstem cells (top). As shown by the mouse at right, an antibody to the angiogenesis-promoting protein VEGF greatly inhibits the growth of glioma stem cell tumors; the mouse at left is an untreated control. CREDIT: S. BAO ET AL., CANCER RESEARCH 66, 7843 (2006)

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 so-called cancer stem cells, Dick suggested, might be what makes the disease so hard to eradicate with radiation or chemotherapy.