Thursday April 30 2009
Low-dose aspirin is used to reduce the risk of blood clots
Daily aspirin in your 40s 'can cut risk of cancer later in life' reported The Daily Telegraph. The newspaper said that people who take the cheap painkiller for 10 years can reduce their risk of breast and bowel cancer. It said that experts say taking aspirin in your mid-40s could be the "best time to stop the disease progressing into full-blown cancer in your sixties”.
The study underlying this report is a review of what is currently known about the benefits, risks and uncertainties of taking aspirin and similar drugs. It found that although research suggests that aspirin can cut the risk of some cancers, it is not currently recommended due to the risk of side effects such as internal bleeding. This risk is compounded by the fact that common cancers tend to develop after the age of 60, when the risk of aspirin causing internal bleeding is at its highest.
The experts conclude that, “only treatment with aspirin combines the benefit of protection against cardiovascular disease with the potential to reduce the risk of some types of cancer, but that more randomised trials are essential.” This seems reasonable considering the current state of knowledge.
Where did the story come from?
Professor Jack Cuzick from the Cancer Research Centre for Epidemiology, Mathematics and Statistics, at the University of London is the first author for this report which was co-authored with 11 other experts, professors and doctors from the US and Europe. Some of the authors declared conflicts of interest by being associated or having received funding from the drug companies Cancer Prevention Pharmaceuticals, AstraZeneca, Lilly Pharmaceuticals or Bayer. The study was published in the (peer-reviewed) medical journal Lancet Oncology.
What kind of scientific study was this?
This publication is an international consensus statement aimed to summarise current research and opinion from experts. The brief was to look at the research to date on the use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) for the prevention of cancer and specifically the balance of risks and benefits.
The authors met at an international Conference on Cancer Prevention in St Gallen, Switzerland in March 2009. In assessing the risks and benefits of NSAIDs, they quickly agreed that aspirin is the only NSAID with sufficient data of its use in general populations. They also established that there are gaps in the understanding of the appropriate dose, duration and age of use of aspirin for cancer prevention, so that a full risk–benefit analysis could not be done. They therefore planned to produce a consensus statement and summary of current knowledge.
The authors say that their paper is not a comprehensive review of the literature, which is available in other reports, but that it summarises a focused discussion of the key outstanding issues. Relevant studies were identified by checking recent comprehensive reviews and by consultation with the panellists.
What does the review say?
The researchers begin by saying that the evidence clearly shows a protective effect for aspirin and other NSAIDs in preventing colorectal cancer and probably other cancer types. However, there are uncertainties in the evidence regarding the balance of risks and benefits when these drugs are used for cancer prevention, so no definitive recommendations can be made.
The researchers discussed the anti-tumour effect of aspirin and other NSAIDs. They concluded that aspirin has emerged as the most likely NSAID for preventing cancer. There is also data showing it reduces the risk of heart disease and some strokes, but also increases the risk of ulcers and internal bleeding.
NSAID drugs work by blocking the effects of proteins that can trigger inflammation and are found at unusually high levels in several types of cancer. Common cancers, such as prostate, breast, lung and bowel, tend to develop after the age of 60, when the risk of aspirin causing internal bleeding is at its highest. This means that the balance of risk and benefit changes as people age, with both changing independently.
The authors say that NSAIDs do delay or prevent bowel and breast cancer in animal models. However, to date, no randomised clinical trials of aspirin or other NSAIDs have looked at preventing cancer deaths in humans. Studies of the mechanisms by which NSAIDs prevent cancer have not provided conclusive evidence but there are theories.
The authors say that most epidemiological observational studies report a reduction of bowel cancer with the use of NSAIDs. Using data from seven cohort studies, they estimate that people in the general population who use long-term aspirin (for about 20 years), will be 15% less likely to develop colorectal cancer (RR 0·85, 95% CI; 0·78 to 0·92). In absolute terms, this means that about 19 men and 16 women out of every 1000, who use the drug to age 74 years would be expected to benefit.
They calculate this expected benefit for other cancers and compare it with the risk of a serious gastric bleed at a similar age. Based on a risk of 0.1% per year the researchers say the excess absolute risk for having a serious bleed is about 24 people out of every 1000 using aspirin to age 74 years.
They go onto discuss other adverse effects and the ongoing debate about the optimal dose for use and whether other drugs might be useful in protecting against ulcers.
What interpretations did the researchers draw?
The researchers conclude that aspirin is the only drug to both protect against heart disease and stroke, and which reduces the risk of some types of cancer.
They suggest that aspirin might eventually be useful for the primary prevention of some cancers in patients who already qualify for low-dose aspirin on the basis of cardiovascular criteria. Also, aspirin or other NSAIDs might be useful in secondary prevention of gastrointestinal cancers in patients who have not already had gastrointestinal bleeding.
The researchers recommend large-scale studies to assess whether long-term aspirin treatment can prevent gastrointestinal and other cancers.
What does the NHS Knowledge Service make of this study?
This paper does not claim to be a comprehensive review of the literature but may be interesting for those needing to decide whether to take aspirin or not. Aspirin is already known to benefit people with heart disease, so an additional benefit in preventing cancer would be a welcome bonus for people already taking on the small risk of bleeding. However, uncertainties remain, especially about the appropriate dose to take and at what age any preventive treatment should begin. Large, long-term studies would help to resolve these uncertainties.