Researchers have identified stem cells in brain cancer tumors that replenish the tumors and keep the

Snuffing out these cancer stem cells could lead to a raft of new treatments for various cancers, according to researchers who published their findings in the Nov. 18 issue of Nature.

Scientists previously identified cancer stem cells in breast cancer tumors, and in leukemia tumors. But no one had found proof of cancer stem cells in other solid tumors until now.

"Now we know this is probably important for other cell cancers as well," said Dr. Peter Dirks, a neurosurgeon and investigator in developmental biology research at the Hospital for Sick Children in Toronto, Canada, "It's not just a one-off in breast cancer or leukemia."

The researchers performed the work, which was funded by the Canadian Cancer Society, by injecting brain tumor cells into mice. They found that the cells initiated and sustained new brain tumor growth in the mice. Brain cancer is one of the deadliest and fast-spreading types of cancer in humans.

"The identification of cancer stem cells is a significant step in the fight against these dreaded diseases. Because self-renewal is essential if tumors are to grow, agents that target such cells may be effective treatments," said Michael Clarke, a professor of internal medicine and cell and developmental biology at the University of Michigan Medical School in Ann Arbor. His commentary was published with the Nature paper.

The researchers achieved their results using 100 tumor cells that carried a marker called CD133. Injecting tens of thousands of tumor cells that lacked the marker failed to produce tumors in the mice.

The goal is to get a single stem cell to grow into a tumor, something Irv Weissman, a professor of developmental biology at Stanford University, has shown in leukemia. If one cell can incite tumor growth, researchers know that's the cell to target if they want to stop the tumor's growth.

Often, cancer tumors respond initially to chemotherapy and radiation treatments, only to grow back again later. Researchers now think that stem cells are responsible for tumor regeneration. If a drug could kill the tumor stem cells specifically, perhaps the tumor would not have the means to grow back, Dirks said.

Cancer stem cells make up a tiny percentage (2 to 5 percent in breast cancer) of all the cells in a tumor, so it's possible scientists have been studying the wrong cells about 95 percent of the time, Dirks said.

The next step, he said, is to find out what makes these cancer stem cells tick, he said.

"Now that we're able to isolate these cells," he said, "we need to find the molecular mechanism -- what genes are being expressed that make them different from the other cancer cells."

Original Article: http://wired.com/news/medtech/0,1286,65735,00.html?tw=wn_tophead_5