The common food poisoning bug salmonella can help the immune system to fight cancer, scientists have discovered.
Acting like a "Trojan horse" the salmonella bacteria can infiltrate tumours and flag the cancer cells up to the body's immune defences, making them a target for attack.
Cancers have evolved ways of evading the immune system and so are often not destroyed.
South Korean researchers have engineered a strain that is a million times less potent than the version of the bug that causes food poisoning.
The team of scientists is now seeking funding for clinical trials as the early animal tests have proved so successful.
In mice with bowel cancer, more than half the animals were completely cured without any side effects.
Professor Joon Haeng Rhee, from Chonnam National University Hwasun Hospital in Jeonnam, South Korea, said: "We believe that this was turning tumour-helping immune cells, Dr Jekyll, into tumour-killing ones, Mr Hyde."
The research reported in Science Translational Medicine is the first time scientists have used the body's own response to salmonella to combat cancer.
The discovery arose from an unrelated study when scientists found that bacteria attacking shellfish produced a protein that triggered a strong immune response.
The modified salmonella releases the same protein to spur the immune system into action.
Professor Kevin Harrington, from The Institute of Cancer Research, London, said: "It has been known for some time that certain types of bacteria, including strains of salmonella, are able to grow in tumours but not in normal tissues.
"However, until now, attempts to use bacteria as anti-cancer therapies have had limited success, both in the laboratory and in the clinic."