Immune system cells recruited by cancers to help them grow and spread could be 're-educated' to attack the tumours instead of aiding them, Cancer Research UK scientists announced at the National Cancer Research Institute (NCRI) Conference in Birmingham.
Interrupting a particular chemical pathway in macrophages - the immune system cells 'hi-jacked' by the cancer - was found to turn them back into cancer killers, capable of attacking the tumour directly and encouraging the rest of the immune system to do the same.
The treatment also significantly reduced the rate of tumour growth in mice with ovarian cancer - an important step in the development of a treatment for human cancer patients.
The findings of the research were presented by Dr Thorsten Hagemann and Prof Frances Balkwill from the Institute of Cancer, Barts and the London, Queen Mary's School of Medicine and Dentistry.
Lead researcher Dr Hagemann said: "Macrophages that are supposed to fight infections typically end up helping cancers by releasing chemical messages that promote tumour growth.
"In fact, 50 per cent or more of a typical cancer will be made up of 'normal' body cells, hi-jacked by the cancer to aid its survival and growth.
"But re-educating the macrophages turned them into effective cancer killers. It also encouraged the rest of the immune system to start acting against the tumour."
Macrophages are known to release chemical messages that activate the protein NF-κB in cells, stopping cell death and promoting cell growth and spread.
But the researchers found that by modifying the chemical signalling pathways in macrophages, they could inhibit the function of NF-κB, stopping it from promoting tumour growth.
When these modified macrophages were exposed to ovarian cancer cells, the macrophages produced nitric oxide - a toxin - which resulted in the cancer cells committing suicide.