Scientists have found evidence that cancerous tumors might originate as stem cells - undifferentiated master cells which can grow into any tissue in the body. Investigators say if this proves true, it could provide a new way to prevent or cure cancer.
Stem cells are primitive structures in the human body that normally transform themselves into healthy, specialized tissue, everything from blood and bone cells to heart and liver cells. Now there is evidence that stem cells can also develop into cancer cells that multiply into life-threatening tumors.
The conventional theory of cancer formation is that it begins with the division of a single mutated cell. The new study challenges this theory with evidence that mutated, cancerous cells may develop directly from stem cells.
Luis Parada, head of developmental biology at the University of Texas Southwestern Medical Center in Dallas, and his colleagues studied an aggressive, lethal form of human brain cancer called glioblastoma multiforme in genetically bred mice. The cancer is usually fatal within a year of diagnosis. Researchers used chemotherapy on the rodents that temporarily halted the growth of their tumors. But when investigators stopped the drug, the cancer came back. Parada says a molecular analysis showed the tumors recurred because a small number of stem cells clustered within the brain tissue began dividing, producing new tumor cells.
But when a group of mice with glioblastoma were given both chemotherapy and a drug that destroyed the stem cells in their brain tissue, their cancer was cured.
Parada says the findings could radically change the way cancer is treated.
“Then it’s no longer valid to evaluate the volume of a tumor and say whether therapy is working or not. What will be important is to know is how that therapy is affecting the cancer stem cells within the tumor,” Parada said.
Two other independent studies published this week provide additional evidence that stem cells may be the starting point for cancerous tumors. One team of researchers from Universite´ Libre de Bruxelles in Brussels, Belgium, and the Wellcome Trust Cancer Research Institute in Britain looked at the role of the master cells in the development of squamous cell carcinoma, a form of skin cancer.
Another group of investigators at the University Medical Center in Utrecht, the Netherlands, engineered a multi-colored model of an intestinal tumor known as an adenoma so they could trace the progression of stem cells to an early-stage tumor. Researchers tagged the master cells with a red color and watched as they produced a protein that stimulated the growth of pre-cancerous blue cells.
Researcher Hugo Snippert, who created the adenoma model, says there can be many genetic mutations in cells that don’t cause cancer. He says it’s only when the stem cells are mutated that cancer develops.
“It’s really essential that you get rid of the cancer stem cells because they are tiny, they are low numbers. But they are able to grow and to give rise and fuel tumor growth really fast,” Snipert said.
University of Texas researcher Luis Parada believes stem cells develop random mutations with age. And he says his lab is studying a potential cure for cancer that would focus on destroying these mutating stem cells as soon as they could be detected.
“And we are very optimistic that in so doing, we are on the verge of discovering viable targets that are unique to these cells,” Parada explained.
He says researchers are still mapping the locations of stem cell clusters in all human organ tissues where cancers are known to develop.
A series of articles on the role of mutated stem cells in the development of cancer are published jointly in the journals Nature and Science.