Aspirin has numerous benefits. It is already known that it may prevent cancer. Research shows it may also be an effective treatment for halting the disease once it has started. An analysis of five large trials of people who took a daily low dose aspirin showed that among those who developed cancer it reduced its spread to distant organs by 40 to 50 per cent.
The spread of cancer, or “metastasis”, is what most commonly kills patients after the disease has been initially diagnosed and treated. The study is one of three published in The Lancet and Lancet Oncology which shows that taking aspirin for as little as two or three years can have a beneficial effect against cancer.
Study leader Professor Peter Rothwell of the University of Oxford and the John Radcliffe hospital said, “It seems likely aspirin will be of benefit when started after cancer is diagnosed.” Studies have previously shown that long-term daily aspirin, for 10 years or so, reduces the risk of colorectal (bowel) cancer and other common cancers, but some experts have voiced concerns over potential long-term side-effects, because aspirin can cause stomach bleeding.
The new studies reinforce aspirin's claim to be a weapon against cancer. They show that taking daily low-dose pills for just three years can reduce the risk of cancer by about a quarter – 23% for men and 25% for women. The risk of dying of cancer is cut by 15% – and by 37% for those who take aspirin for longer than five years. All the data came from 51 trials giving low-dose aspirin to people at risk of a heart attack or stroke. Aspirin thins the blood, making it less likely to clot.
The second study found that aspirin helped prevent the spread of cancer – or metastasis – to other organs, which is a serious threat to the patient's survival. Aspirin reduced the proportion of cancers that spread instead of staying localized by 48%. The drug also reduced the risk of being diagnosed with a solid cancer that had already spread by 31%. For patients initially diagnosed with a local cancer, the risk of later metastasis was reduced by 55%.
Aspirin's ability to slow metastasis may be linked to its effect on platelets, the clotting bodies in the blood, said the scientists. The role of platelets in promoting cancer spread in mice was reported more than 40 years ago. Rothwell said the effect of aspirin on the spread of cancer was unique and might be useful in treatment. “Previously, no drug has ever been shown to reduce metastasis as a specific effect,” he said. “It opens up a completely new therapeutic area.”
Rothwell said it was time to think again. “It's certainly time to add prevention of cancer into the analysis of the balance of risk and benefits of aspirin. So far, all the guidelines have just been based on the prevention of strokes and heart attacks. This research really shows that the cancer benefit is as large, if not larger, than the benefit in terms of preventing heart attacks and strokes. It does change the equation quite drastically.”
A spokeswoman for the Department of Health said, “We are currently considering how to ensure the public gets the best advice on this issue, given that there are risks as well as potential benefits from taking aspirin.”
Rothwell suggested that the National Institute for Health and Clinical Excellence, which issues treatment guidelines for the NHS, should issue advice on the use of aspirin to combat cancer. “I think it would be helpful in the fullness of time if a body like Nice, for example, would come up with an independent recommendation on the basis of all the evidence that has been gathered,” he said. “That would give people confidence.”
Nice has never been asked by the department to develop guidance on aspirin and cancer prevention. But the drug is mentioned in the latest Nice guidance on colorectal cancer. It says that “regular use of non-steroidal anti-inflammatory drugs (NSAIDs), notably aspirin, seems to reduce the risk of colorectal cancer”.
Two American experts commenting in The Lancet pointed out some limitations to the research. Dr Andrew Chan and Dr Nancy Cook, from Harvard Medical School in Boston, said the analysis did not include findings from two large US trials that failed to show an anti-cancer benefit from taking aspirin every other day. Some analyses were also limited by the quality of available data. However the US experts concluded, “These caveats notwithstanding, Rothwell and colleagues show quite convincingly that aspirin seems to reduce cancer incidence and death.”
But despite this compelling evidence, Professor Rothwell urged patients not to start taking aspirin every day purely to try to prevent cancer. Aspirin can have harmful side effects including stomach ulcers and internal bleeding in the intestines. Other risks in adults include kidney disease and tinnitus – or ringing in the ears. But he said that the thousands of patients currently taking aspirin to prevent heart attacks and stroke would almost certainly be also reducing their risk of dying from cancer.
Professor Peter Johnson, Cancer Research UK’s chief clinician, said, “This is an exciting development. It adds to the other established ways of reducing cancer risk – not smoking, keeping a healthy bodyweight and cutting down on alcohol. It’s a good idea for people thinking of taking aspirin to discuss it with their GP, as it can sometimes have side effects such as internal bleeding especially in people over 70. The research also suggests that aspirin may help to prevent cancer from spreading in the body, so it could be beneficial for people already diagnosed with cancer.” “However, because of the risk of bleeding, patients should discuss this with their specialist before starting to take aspirin, and be aware of the potential for increased complications before surgery or other treatments such as chemotherapy,” he said.
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