While scientists hotly debate the existence of cancer stem cells, three related new studies, all conducted on mice, provide some supporting evidence. Stem cells are the foundation for healthy cell growth in the body. Some researchers believe that malignant stem cells also exist—so-called cancer stem cells that generate tumors and resist treatment by simply re-growing afterward. "Cancer stem cells are still controversial, but with progress in studies like these, it's less about whether they exist and more about 'what does this mean?'" said Dr. Max Wicha, director of the University of Michigan Comprehensive Cancer Center, who is familiar with the...