Monday September 28 2015
Aspirin: a powerful pill, but not yet proven as a cure for cancer
"Aspirin could almost double your chance of surviving cancer," the Daily Mail reports, with most of the newspapers featuring similar claims.
According to the Mail: "Three quarters of people with bowel, stomach or throat cancer were still alive five years later, and aspirin is the 'magic bullet' that should be prescribed as soon as someone is diagnosed."
Unfortunately, the claims appearing in the media are based solely on a press release and abstract of research being presented at a scientific conference. This means the results and conclusions won’t have been verified by independent experts and we don’t have all the information to appraise such research. For these reasons, we need to be cautious about this finding.
Compounding our scepticism over these reports are apparent inconsistencies between the sources used to compile the stories, including survival figures we cannot verify from the information available.
It’s also worth noting that the type of study means we can’t prove aspirin itself was improving people’s chances of surviving gastrointestinal cancer.
With those notes of caution in mind, and as further information comes to light, it may be the case that this is a cheap, readily-available drug that can be used to help people diagnosed with cancer to survive longer.
However, it should be noted that the researchers have not found that taking aspirin can stop you getting cancer. Also, taking aspirin regularly carries a risk of side effects, such as internal bleeding. It would need to be ensured that the benefits of the drug in terms of cancer survival outweighed these risks.
Where did the story come from?
The stories follow a conference abstract and accompanying press release related to a study due to be presented at The European Cancer Congress 2015.
This congress is described as the largest European platform for presenting groundbreaking cancer research to a global audience, renowned for presenting practice-changing information.
The study being presented was conducted by researchers from Leiden University Medical Centre, and other oncology research centres in The Netherlands. The researchers report no conflicts of interest.
The media coverage would benefit from highlighting the limited information available so far, and that this is not a published study.
What kind of research was this?
The study in question is a retrospective cohort study that looked back at a cancer registry of people with cancers of the gastrointestinal tract (the mouth, oesophagus and so on, out to the rectum) and looked at how taking aspirin after diagnosis and was linked to survival.
Previous research has suggested a relationship between aspirin and possible preventative and therapeutic effects for cancer. However, the biological mechanism by which aspirin could be having these effects is controversial. A previous study also focused solely on bowel cancer, while this study looked at all gastrointestinal tract cancers.
As this is a retrospective observational study rather than a prospective trial randomising people to aspirin use or not, it cannot prove aspirin as being the cause in difference in survival.
However, as information on this trial is so far only available as a conference abstract, without full publication of the study in a peer-reviewed journal it is not possible to give a full critique of the design, methods and implications.
What did the research involve?
The researchers say they used the population-based Eindhoven Cancer Registry to identify all people with a cancer of the gastrointestinal tract diagnosed between 1998 and 2011. These people were then linked to drug dispensing data from the PHARMO Database Network (the Institute for Drug Outcomes Research) to identify whether they had used aspirin after their cancer diagnosis.
Researchers noted whether each person used or did not use aspirin in particular time periods. Overall survival for people in the cohort was compared with expected survival in the general population.
What were the basic results?
The study featured 13,715 people with a gastrointestinal tract cancer. Just under a third of them had used aspirin before cancer diagnosis, just under two-thirds were non-users, and just under 1 in 10 had solely used aspirin after cancer diagnosis.
The analysis focused on comparing the non-users with the post-diagnosis users only. The majority of all of these people had bowel or rectal cancer, and the remaining 10% had oesophageal cancer.
The abstract says that average follow-up time for all patients was just over two years. The researchers reported that five-year survival was 56%, but did not report how this differed between people who used or did not use aspirin. The researchers say they are providing more information on comparative survival rates at the congress.
The accompanying press release provides more specific data, but it appears inconsistent with that presented in the abstract.
In the press release, the researchers say: "[Average] follow-up time for all patients was 48.6 months, with 28% of patients surviving for at least five years. Patients using aspirin after their diagnosis had a chance of survival twice as high than that of those who did not use it in the same circumstances.
"The beneficial effect of aspirin use on survival was seen in patients with [gastrointestinal] tumours after adjusting for potential confounding factors such as sex, age, stage of cancer, surgery, radiotherapy, chemotherapy and other medical conditions or disorders."
How did the researchers interpret the results?
The researchers conclude: "Aspirin use initiated after diagnosis of gastrointestinal malignancies is associated with higher overall and relative survival rates."
This large observational study, which is being presented at The European Cancer Congress 2015, used official data to look at whether using aspirin after being diagnosed with gastrointestinal cancer influenced survival in a population.
Because the results are only available as a brief conference abstract and press release, and given the apparent discrepancies between the sources, it is difficult to give further appraisal or interpretation of the results. Publication of the study in a peer-reviewed journal is needed to be able to understand the strengths and limitations of this study.
The main limitation was that it is only an observational study. However, it is apparently large and – according to the abstract – is likely to have accounted for potential confounders. Despite this, it may still be difficult to pin any effect on survival directly on the action of aspirin, rather than other factors associated with aspirin use.
A randomised controlled trial, where people with a new cancer diagnosis are randomly told to take (or not take) aspirin, would better balance out any differences between the study population and would be more reliable for looking at the direct effects of aspirin.
The researchers say there is a new trial currently in action in the Netherlands that has randomised elderly people with bowel cancer to take daily aspirin or placebo. This may provide more convincing evidence of a benefit from aspirin treatment.
If these combined studies are positive, as lead researcher Dr Frouws says: "Given that aspirin is a cheap drug with relatively few side-effects, this will have a great impact on healthcare systems, as well as patients".
The scientific co-chair of ECCO, Professor Peter Naredi, who was not involved in the research, says in the press release: "We have good evidence that the frequent use of aspirin in the population can prevent some cases of [bowel] cancer ... With more and more data to support the beneficial role of aspirin, we must consider whether we should recommend it to a wider public."
The evidence for aspirin in cancer seems to be going in a promising direction, but given the unpublished status of all this evidence, it is too early to suggest aspirin as a "magic bullet" for improving gastrointestinal cancer survival.