Too often, the cancer seems to have been erased by the processing returns. Some scientists have blamed so-called cancer stem cells, a subset of cancer cells that may be able to remain dormant, evading chemotherapy or radiation to form months or years, new tumors later. The idea was controversial but today published three documents to prove that in certain brain, skin and intestinal tumors, cancer stem cells are the source of tumor growth.
The model of cancer stem cells is different from the traditional idea that tumor growth is equality of opportunity which is all and all cancer cells can divide and cause a tumor to grow and propagate. The stem cell model assumes that the growth of the tumor is hierarchical, mainly driven by a subset of cells that can make new copies of themselves and give rise to other types of tumor cells contains. Some of the first evidence for cancer stem cells come from leukemia studies in the 190s showing that only a small part of cancerous blood cells could spread the disease in mice. But it was difficult to determine whether cancer stem cells fuel the growth of tumors in other tissues.
In the new study, three independent groups used genetic cell labeling techniques to trace the proliferation of certain cells in the tumors to grow. The method gives researchers a glimpse of "what happens in the real life of a tumor," explains Cédric Blanpain, stem cell researcher at the Free University of Brussels in Belgium. He and his colleagues report online Nature that in tumors papilloma mouse, a precursor of skin cancer, most of the tumor growth came from a few cells, which in some ways resembled the stem cells that maintain healthy skin.
In a second article, also published online today in Nature , developmental biologist Luis Parada and his colleagues at the University of Texas Southwestern Medical Center (UTSMC) show in Dallas than in mice that develop glioma, a form of brain cancer, the growth of the tumor appears to be from a small subset of cells in the tumor. They found that the cells may remain dormant for chemotherapy that kills most cancer and may give rise to new tumors after drug treatment stops.
And in the third paper, published online today in Science , developmental biologists and researchers on stem cells Snippert Hugo, Arnout Schepers, Hans Clevers, and their colleagues the Hubrecht Institute in Utrecht, Netherlands, used mice with multicolored intestines watching the cell types that form the intestinal adenomas, a precursor to intestinal cancer. Rodents, scientists have nicknamed confetti mice are genetic markers that can label the intestinal cells blue, green, red or yellow according to the cell where they come from. The team reports that adenomas develop from cells that express a gene called LGR5 + , which is also active in normal intestinal stem cells. "The tumor is really like a caricature of normal tissue," said Snippert.
These cell tracing techniques are the right approach to test the model of cancer stem cells, said Sean Morrison, who studies stem cells and cancer UTSMC and has not been involved in any studies. There is now enough evidence to be pretty sure that the model explains at least some types of cancer, he said. Morrison warns, however, that studies of papilloma and adenoma looked precancerous tumors. Indeed, when Blanpain and colleagues examined mice with squamous cell carcinoma, a malignant growth papilloma, they found that most of the cells were actively dividing, not just a small subset of stem cell-like cells .
Understanding cancers that can develop from or simply harbor-cancer stem cells is key to more effective treatments, researchers say. This is not an easy task, however. Morrison notes that the growth of tumors differs even in patients with the same cancer. Still, says Parada, with three examples where tumors appear to harbor cancer stem cells suggests that there will be more. "I hope will strengthen and stimulate community" to understand how to better study the model of cancer stem cells, he said. "We will bring this level of control in all solid tumors."
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