Cancer treatments could be more effective when they are combined with aspirin, a British study has suggested.
The anti-inflammatory pain killer was found to suppress a cancer molecule that allows tumours to evade the body's immune defences.
Experts said the research findings were "exciting" and suggested that drugs which cost just a few dollars could make "a huge difference".
But they cautioned that the findings would need to be confirmed by further trials before aspirin was routinely given as part of cancer treatment. Laboratory tests showed that skin, breast and bowel cancer cells often generated large amounts of a molecule called prostaglandin E2 (PGE2).
The study found that aspirin and other members of the "Cox inhibitor" drug family block its production, leaving tumours exposed to attack.
In tests on mice, immunotherapy combined with drugs such as aspirin substantially slowed the growth of bowel and malignant skin cancer.
Prof Caetano Reis e Sousa, who led the team from the Francis Crick Institute in London, said: "We've added to the growing evidence that some cancers produce PGE2 as a way of escaping the immune system.
"If you can take away cancer cells' ability to make PGE2, you effectively lift this protective barrier and unleash the full power of the immune system."
The ability of cancers to manufacture PGE2 may be one reason why some experimental immunotherapy treatments have not lived up to expectations.
Professor Peter Johnson, chief clinician at Cancer Research UK, which funded the study, published in the journal Cell, said: "PGE2 acts on many different cells in our body and this study suggests that one of these actions is to tell our immune system to ignore cancer cells.
"Once you stop the cancer cells from producing it, the immune system switches back to 'kill mode' and attacks the tumour.
"This research was carried out in mice so there is still some way to go before we will see patients being given Cox inhibitors as part of their treatment. But it's an exciting finding that could offer a simple way to dramatically improve the response to treatment in a range of cancers."
Daily Telegraph UK