This can turn a non-toxic substance called 5-fluorocytosine into a nasty chemical called 5-fluorouracil that kills all cells, normal and malignant.

ECONOMIST: Cancer treatment

Cancerous rats were then given both 5-fluorocytosine, which circulated throughout their bodies, and genetically tinkered stem cells, which made their way straight to the gliomas.

ECONOMIST: Cancer treatment

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