Aspirin may be able to boost the effectiveness of cutting-edge cancer medicines that bolster the immune system, scientists say.
Immunotherapy lets the body's own defences fight cancer and has been a source of huge excitement in the field.
And now scientists at the Francis Crick Institute have published a study suggesting aspirin may prevent tumours from hiding from the immune system.
Cancer Research UK said it could be a simple way of improving treatment.
The team showed that skin, breast and bowel cancer cells were producing high levels of a chemical, called prostaglandin E2, that could dampen down the immune response - effectively letting a tumour hide.
However, drugs like aspirin are able to change the chemical pathways inside the cancer cells that lead to prostaglandin E2 being produced.
Experiments in mice, published in the journal Cell, suggest such drugs can boost immunotherapy treatment.
But Prof Caetano Reis e Sousa, one of the researchers, told the BBC News website: "We are very far off patients, all this is preclinical research in mouse models, what we would like to do now is set up a clinical trial to formally demonstrate this could happen in humans."
Immunotherapy is one of the most promising fields in cancer research, with some trials showing terminal cancers can be shrunk and even disappear completely in rare cases.
Prof Reis e Sousa added: "The findings are exciting in the context of renewed interest in immunotherapy, really everyone in oncology and immunology has become extremely excited.
"But what we're finding is not a revolution, it's an evolution [that could help us] try to achieve an even greater rate of remission."
There have been previous suggestions that aspirin can prevent cancers forming in the first place.
And Prof Reis e Sousa said it was possible that aspirin was also preventing cancers forming by acting on the immune system, but that was still untested.
Prof Peter Johnson, from Cancer Research UK, said: "This research was carried out in mice, so there is still some way to go.
"But it's an exciting finding that could offer a simple way to dramatically improve the response to treatment in a range of cancers."