Mice resistant to cancer have been created in a breakthrough that could lead to a human treatment free of side-effects.
A protein produced by the creatures may hold the key to a future therapy.
It attacks tumour cells, but does not harm healthy tissue in the body.
Scientists hope it can one day be adapted for use in humans - saving them the pain, nausea and hair loss usually associated with cancer treatments.
The breakthrough hinges on a mouse gene called Par-4, which produces the protein. U.S. researchers genetically engineered a group of mice to have higher levels of the protein than normal.
These creatures were found to be immune to many forms of the disease, such as cancer of the liver and prostate, the journal Cancer Research reports.
Tests suggest the protein could also beat off breast, pancreatic and head and neck cancers.
Crucially, the animals did not suffer any visible side-effects, the U.S. scientists said.