A way of destroying cancers with our own immune system is a long-held goal of medicine. Now a new twist on such immunotherapy has given promising results in mice.

The treatment is a gel sprayed on to the wound left when a tumour is cut out. The targeted delivery means nearby immune cells start killing cancer cells, both at the wound and elsewhere in the body – but it doesn’t cause a potentially harmful body-wide immune reaction

Several kinds of immunotherapy have been …