Image caption Cancer stem cells (in green) seen in action for the first time

Researchers have discovered the cells in tumours that seem to be responsible for the regrowth of tumours.

Three separate studies on mice appear to have confirmed the view that the growth of tumours is driven by so-called cancer stem cells.

The researchers claim to have resolved one of the biggest controversies in cancer research and say their work marks a "paradigm shift" in the field.

The studies have been published in the journals, Nature and Science.

Doctors often successfully reduce the size of tumours through various therapies, but often patients suffer a relapse and the tumour regrows.

Some researchers believe that this happens because therapies fail to eradicate a small proportion of cells that drive tumour growth known as cancer stem cells. They believe that these are the cells that should be targeted to eliminate the tumour forever.

Evidence for the existence of cancer stem cells has been weak. But now three separate groups of researchers working independently have found direct evidence of cancer stem cells driving tumour growth in brain, gut and skin cancers.

The suggestion is that the same may be true of all cancers which produce solid tumours.

We have shown for the first time there is such a thing as a cancer stem cell and that tumours are maintained by them Prof Hugo Snippert , University Medical Centre in Utrecht

According to Prof Cedric Blanpain of the Free University of Brussels, who led one of the studies, the results could pave the way for a new approach to treating many cancers.

"If these cells are indeed the cells that fuel tumour growth then maybe you can target these cells," he told BBC News.

But that may be easier said than done. The newly-identified cancer stem cells are very similar to healthy stem cells responsible for growing and renewing tissue in the body. Any therapy to target cancer stem cells may also destroy healthy tissues. A priority for researchers will be to see if there are important differences between normal and cancer stem cells so that therapies can distinguish between them.

But according to Prof Hugo Snippert of the University Medical Centre in Utrecht, who led the study into intestinal tumours, the confirmation that these cells exist is an important step in future cancer research.

"Many argued that these cells did not exist. But we have shown for the first time there is such a thing as a cancer stem cell and that tumours are maintained by them," he said.

Prof Luis Parada of the University of Texas, who led research that identified stem cells in brain tumours in mice, said he believed there would now be a new approach to developing new treatments for solid tumour cancers.

"Cancer stem cells change the paradigm. The goal of shrinking tumours may well turn out to be less important than targeting the cancer cells in that tumour."

Dr Michaela Frye, a Cancer Research UK scientist based at the University of Cambridge, said: "These results add even more weight to the theory that cancers are driven by a distinct group of cells called cancer stem cells. Because cancers are proving to be so complex, we don't yet know how relevant this research in mice is to humans, but it gives us new insights into how cancers might develop and why they can sometimes grow back after therapy."

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