Monday September 10 2007
Can aspirin cut cancer risk by 25%?
Using aspirin can reduce the risk of breast cancer by 25%, The Daily Telegraph and the Daily Mirror reported. The Mirror reported that women who regularly use it had a “statistically significant drop in risk of breast cancer”. Both newspapers included a caveat however, that high doses would be needed to achieve this, and this would in turn raise the risk of gastric bleeding – a possible side-effect of this type of drug.
The story is based on a case-control study which found that women who have breast cancer were less likely to have taken quite high doses of non-steroidal anti-inflammatory drugs (NSAIDs) (such as ibuprofen and aspirin) in their lives than women who don’t have breast cancer.
This is a well conducted study. However, by virtue of its design, there are some weaknesses to highlight. Importantly, as the researchers mention, there are significant harms associated with use of high doses of this type of drug. The dangers of NSAIDs include an increased risk of internal bleeding, some types of stroke and stomach damage. More research is needed before women consider increasing their intake of these drugs.
The study’s authors acknowledge the ongoing research into using these drugs to prevent a range of different cancers. Hopefully, one result of this research will be to answer the question: if these drugs do have an effect, what is the optimal dose to maximise the benefit and minimise the harm?
Where did the story come from?
Doctor Victoria Kirsch and colleagues from Cancer Care Ontario in Canada carried out this research. It is unclear who funded the study. The study was published in the peer-reviewed medical journal, American Journal of Epidemiology.
What kind of scientific study was this?
The study was a case-control study in women from Ontario aged 25 to 74 years with and without breast cancer. Researchers identified 3,125 women who were diagnosed with breast cancer between 1996 and 1998 from medical records. Another group of 3062 women who didn’t have breast cancer and were similar to the first group in terms of age were then identified.
A questionnaire and a $5 incentive were mailed to both groups of women to gather information on breast cancer risk factors, smoking, migraines, arthritis and over-the-counter or prescription medication use. The researchers then compared use of NSAIDs between the two groups to see whether there was a link between having breast cancer and use of these anti-inflammatory drugs.
What were the results of the study?
The researchers found that women who were ‘regular’ NSAID users, (defined as those who had used NSAID medication daily for longer than 2 months to control pain or inflammation) were 24% less likely to have breast cancer.
The researchers also found that the relationship between NSAIDs and cancer risk was not affected by whether the women were hormone receptor positive or negative. This finding doesn’t support the view suggested by some studies that the drugs may offer greater benefit for receptive-positive tumours because of the way they act at a cellular level. Similarly, there is a theory that smokers may have a greater reduction in risk than non-smokers because of the chemicals and processes involved at a cellular level. This was not confirmed by this study.
What interpretations did the researchers draw from these results?
The researchers say that their study found that using high-dose NSAIDs for chronic pain or inflammation was associated with a reduced risk of breast cancer. They highlight the fact that this finding was regardless of smoking status or arthritis (one particular indication for use of NSAIDs) and that it applied to both hormone receptor positive and hormone receptor negative breast cancer.
What does the NHS Knowledge Service make of this study?
This is a well conducted study. We highlight the following limitations, many of which are associated with this type of study design:
- Only 73% of women with cancer and 61% of those without returned their questionnaires. We have no way of knowing how different those who didn’t respond were from those who did.
- Another potential weakness is that the researchers relied on the participants to remember what drugs they had used in the past. It is unlikely that all women would have been able to accurately remember what medications they had taken throughout their lives.
- The researchers attempted to adjust for things that may affect the risk of breast cancer or be linked to the use of NSAIDs, such as HRT use, age, family history of breast cancer, physical activity, BMI etc. However, there are other factors that they didn’t consider, such as diet and other indications for using the anti-inflammatory drugs. These other factors may modify the relationship between NSAID use and breast cancer status.
- A previous study, based on a randomised controlled design found that low dose NSAIDs had no effect on breast cancer risk. However, as the researchers here point out, women in their study were taking much higher doses.
Importantly, there are harms associated with higher doses of these drugs, including bleeding, some types of stroke and damage to the stomach. Women should not change their use of these drugs on the basis of this study and should consult their doctor if they are thinking of doing so. It is currently uncertain what dose of NSAIDS women should take to derive the benefits that are seen in this study.
Sir Muir Gray adds…
Aspirin is a wonderful drug and the results from similar studies have suggested that aspirin reduces the risk of bowel cancer. However, at present an aspirin a day cannot be recommended as a means of keeping cancer away.