At a laboratory in Baltimore, hairless mice kept in racks of plastic crates are labelled with yellow cards, each identifying a person fighting cancer. These mice are cancer “avatars”—the lumpy tumors visible under their skin come from actual patients.
The animals serve as personalized, living test tubes. Each mouse will eventually be treated with a different drug and its tumors measured. Results showing which medicine worked best will be sent back to a doctor trying to treat a difficult cancer case.