Since the protein needed to transform 5-fluorocytosine could only be churned out by souped-up stem cells, only the gliomas were exposed to the poison, killing them but sparing normal tissue, which the stem cells ignored.

ECONOMIST: Cancer treatment

Tissue cells, instead of performing the normal self-repair of damaged tissue, begin laying down excessive layers of collagen to help build a scar.

FORBES: Scar Wars

"We're already using the fact that 5t4 is found in cancer cells, but not in normal tissue, to design immunotherapy against it and are testing two such systems in clinical trials, " said Professor Stern.

BBC: NEWS | Health | Molecule 'helps cancer to spread'