Long-term, low-dose aspirin use may cut bowel cancer risk
Long-term use of low-dose aspirin could reduce the number of cases of bowel cancer and deaths from the disease, British scientists have found.
High-dose aspirin has previously been shown to reduce the incidence of bowel cancer, but regularly taking the drug at these levels can cause serious side effects like gastrointestinal bleeding and ulcers.
The latest research - conducted by scientists from the University of Oxford, the University of Edinburgh, the London School of Hygiene and Tropical Medicine, Sweden and The Netherlands - indicates that lower doses of aspirin could be effective. This may reduce the risk of unwanted side effects, though the precise level of risk still needs to be confirmed.
The study, published in the Lancet medical journal, suggests that a low daily dose of aspirin could prevent a quarter of cases of bowel cancer and reduce mortality by more than a third.
The team carried out a 20-year follow-up of five randomised trials, including four that compared low-dose aspirin (75 to 300mg per day) with a placebo (dummy pill), and one trial of different doses of aspirin.
In the first four trials, 391 out of 14,033 patients (2.8 per cent) developed bowel cancer over an average follow-up of 18.3 years.
Aspirin was found to reduce the 20-year risk of bowel cancer by 24 per cent, and the risk of dying from bowel cancer by 35 per cent.
The results suggested that aspirin predominantly helps to prevent proximal bowel cancer (high up in the bowel), along with some cases of cancer of the rectum (back passage). But it does not seem to have such a marked effect on distal (lower) bowel cancer.
The study authors noted that the five trials were carried out before recent results about using sigmoidoscopy or 'Flexi-scope' screening for bowel cancer were published, and that the two interventions could complement each other in preventing bowel cancer.
They concluded: "The suggestion of a particular effect of aspirin on more aggressive and rapidly growing tumours might allow less frequent screening, and the prevention of proximal colonic cancers by aspirin, which would not be identified by sigmoidoscopy, is clearly important.
"It is therefore probable that these two approaches to prevention of colorectal cancer will be synergistic."
Commenting on the findings, lead researcher Professor Peter Rothwell, from John Radcliffe Hospital and the University of Oxford, said that the two approaches could "substantially" reduce the incidence of bowel cancer.
The government recently announced that the Flexi-scope test will be incorporated into the NHS bowel cancer screening programme.
Writing in an accompanying editorial, Drs Robert Benamouzig and Bernard Uzzan from Avicenne Hospital in France said: "This interesting study would incite clinicians to turn to primary prevention of colorectal cancer by aspirin, at least in high risk-populations. Specific guidelines for aspirin chemoprevention would be the next logical step."
Dr Alison Ross, senior science information officer at Cancer Research UK, said: "This is the first large study to show that low doses of aspirin may be effective in protecting against bowel cancer. This is exciting since lower doses are less likely to cause potentially serious side effects, such as bleeding in the digestive system. Once it's confirmed that the benefits of taking low-dose aspirin outweigh the risks, clear guidelines will be needed to help doctors inform their patients about long-term use. Anyone considering taking aspirin regularly should first seek advice from their GP."
- Rothwell, P., Wilson, M., Elwin, C., Norrving, B., Algra, A., Warlow, C., & Meade, T. (2010). Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials The Lancet DOI: 10.1016/S0140-6736(10)61543-7