The Cardiff University team discovered a method of killing prostate, breast, lung and other cancers in lab tests.
Experts said that although the work was still at an early stage, it was very exciting.
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.