An aspirin pill a day can increase the survival chances of people with common cancers by a fifth, research has shown.
Scientists made the discovery after analysing a wealth of available data from studies of bowel, breast and prostate cancer.
They found that patients who took low-dose aspirin in addition to receiving their usual treatment reduced the likelihood of dying by 15% to 20% over an average period of five years.
Professor Peter Elwood, from the University of Cardiff, who led the research published in the journal Public Library of Science ONE, said: "There is a growing body of evidence that taking aspirin is of significant benefit in reducing some cancers.
"Whilst we know a low dose of aspirin has been shown to reduce the incidence of cancer, its role in the treatment of cancer remains uncertain. As a result, we set out to conduct a systematic search of all the scientific literature."
The team pooled together data from five randomised trials and 42 observational studies.
As well as improving survival, aspirin appeared to reduce the risk of cancer spreading.
Although a known risk associated with taking aspirin is bleeding in the gut, the researchers found no evidence of this being serious or life-threatening.
The study highlights the need for trials to establish whether low-dose aspirin really should be considered an additional treatment for cancer, said the researchers.
Professor Elwood added: "While there is a desperate need for more detailed research to verify our review and to obtain evidence on less common cancers, we'd urge patients diagnosed with cancer to speak to their doctor about our findings so they can make an informed decision as to whether or not they should take a low-dose aspirin as part of their cancer treatment."
Studies of six other cancers also suggested an aspirin benefit, but in these cases patient numbers were too low to allow confident interpretation of the data.