Scientists discover why brain tumours are difficult to treat

These stem cells can regrow a tumour with only a handful of cells left behind which explains why the tumours, called glioblastomas, are so difficult to treat, said study researcher Inder Verma, a molecular biologist at The Salk Institute in California.

Even the surgical removal of a tumour may not be able to extract every single cancerous cell, Verma told LiveScience.

Glioblastomas "reoccur because every cell that is left behind has the ability to start all over again," Verma said.

Using viruses, researchers introduced cancer-causing genes into mice, developing a technique in which as few as 20 cancerous cells can trigger tumour growth.

They then found that a mere 10 cells from one of these mouse tumours, transplanted into a healthy mouse, could lead to a whole new tumour in that mouse.

"That suggested that every cell in these tumours or glioblastomas has the ability to make new glioblastomas," Verma said.

Researchers once believed that glioblastomas arose only from glial cells, the "support" cells in the brain that surround neurons.

When it was discovered that the brain contains stem cells, which are capable of transforming into any sort of neural tissue, researchers figured cancer could arise from those cells, too, said researcher Dinorah Friedmann-Morvinski, also a Salk Institute researcher.

The team found that neurons, which should not be able to divide and reproduce anymore, turn back into stem cells, which can continuously divide.

The next step, the researchers said, is to learn more about how the cells revert into stem cells and then find a way to block the out-of-control growth of these cancerous cells.

"You have to kill them in order to kill the tumour in the long run," Verma said.

The study was published in the journal Science.