What have they found?
Our immune system is our body's natural defence against infection, but it also attacks cancerous cells.
The scientists were looking for "unconventional" and previously undiscovered ways the immune system naturally attacks tumours.
What they found was a T-cell inside people's blood. This is an immune cell that can scan the body to assess whether there is a threat that needs to be eliminated.
The difference is this one could attack a wide range of cancers.
"There's a chance here to treat every patient," researcher Prof Andrew Sewell told the BBC.
He added: "Previously nobody believed this could be possible.
"It raises the prospect of a 'one-size-fits-all' cancer treatment, a single type of T-cell that could be capable of destroying many different types of cancers across the population."