Wednesday April 25 2012
It's unclear why aspirin users survived bowel cancer for longer
The risk of dying from bowel cancer can be “slashed by taking an aspirin a day”, according to the Daily Mirror.
The news is based on a large Dutch study that examined the medical records of bowel cancer patients to see whether they had used aspirin before and after diagnosis. It found that those who used aspirin frequently after their diagnosis had a 33% greater chance of surviving for at least nine months than patients who had not been prescribed the drug or who only used the drug infrequently after diagnosis. The association between aspirin and improved survival rates was strongest in elderly patients who were not having chemotherapy.
The findings of this large study are noteworthy and add to those of a growing number of studies looking at whether the humble aspirin pill can prevent or treat cancer. However, the design of this particular study means it cannot prove that aspirin reduces the risk of dying in patients diagnosed with bowel cancer. One important limitation is the likelihood that many of the patients in the study were taking prescribed aspirin as a treatment for heart disease and stroke rather than for bowel cancer, which might distort the survival rates seen. This is particularly a problem as the study simply recorded who died, and not what they died from. Controlled trials comparing aspirin users to similar participants not using the drug will be needed to prove any benefit of aspirin for bowel cancer.
Aspirin can have side effects, including intestinal bleeding, and in cancer patients it can increase the chances of complications before surgery and other cancer treatments. Given the potential for side effects, anyone who wishes to take aspirin with a view either to prevent or treat cancer should consult their doctor before doing so.
Where did the story come from?
The study was carried out by researchers from Leiden University and other institutions in the Netherlands. There is no information about whether it received any external funding. The study was published in the peer-reviewed British Journal of Cancer.
The study was covered fairly in the media, and most papers featured expert advice reminding the public that it is too soon to recommend aspirin as a method of either preventing or treating cancer.
What kind of research was this?
In recent months, several high-profile studies have looked at whether aspirin can reduce the risk of developing cancer, including bowel cancer, in people genetically susceptible to the condition.
This latest observational study looked for any association between aspirin and improved survival in patients diagnosed with bowel cancer. As an observational study, it cannot tell us whether aspirin actively reduced the risk of death in these patients, but only that aspirin use was associated with improved survival rates. A randomised controlled trial would be needed to tell us whether aspirin use directly caused changes in people’s chances of survival.
The researchers point out that bowel cancer (also called colorectal cancer) is one of the most common cancers in the developed world, with 1 million new cases and 600,000 deaths worldwide annually. Previous research has found that regular use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) may reduce the risk of bowel cancer. However, it is not clear if aspirin use can influence survival rates for people already diagnosed with the disease.
What did the research involve?
The study included patients in a large cancer registry for the southern area of the Netherlands, who had been diagnosed with bowel cancer between 1998 and 2007. To find out about survival in these patients, the researchers looked at population registries linked to the cancer registry data.
They looked at prescriptions of aspirin and other NSAIDs for these patients, which were recorded on a large national database linked to the registry. They looked at what dosage of aspirin and other NSAIDs was prescribed and whether they were dispensed before diagnosis, after diagnosis or both before and after diagnosis. From this information, they classified bowel cancer patients into:
- non-users – who never used prescribed aspirin or other NSAIDs, or who had a prescription for less than 14 days
- users – who had a prescription for at least 14 days
- frequent users – who had at least three prescriptions within nine months
Users were also classified as:
- those who had used aspirin before and after diagnosis
- those who used aspirin before diagnosis only
- those who used aspirin after diagnosis only
They also classified the results according to whether patients had colon or rectal cancer, which each affects a different part of the bowel, and whether they had used aspirin, another NSAID or both. They adjusted their results for other factors that might have influenced survival, including sex, age, presence of other illness and stage of cancer.
What were the basic results?
In total, 4,481 patients diagnosed with bowel cancer from 1998 to 2007 were included in the study. Almost two-thirds (62%) were diagnosed with colon cancer. Of the 4,481 diagnosed with bowel cancer, 26% had never had any prescriptions for aspirin or other NSAIDs, 47% had prescriptions for the drugs both before and after diagnosis and 27% had prescriptions only after diagnosis. Most prescriptions for aspirin were at a daily dose of 80mg.
The researchers found that, compared with bowel cancer patients who were non-users of aspirin, those who used prescription aspirin only after diagnosis had a 33% greater chance of surviving for at least nine months (adjusted rate ratio [RR] 0.77, 95% confidence interval [CI] 0.63 to 0.95).
When they classified patients according to type of cancer, they found the survival benefit was only for colon cancer (adjusted RR 0.65, 95% CI 0.50 to 0.84).
For frequent users, the survival gain associated with aspirin use was 39% greater, compared with non-users (adjusted RR 0.61, 95% CI 0.46 to 0.81).
Those who used aspirin both before and after diagnosis had a 12% lower chance of dying than non-users.
Using other NSAIDs was associated with decreased survival (adjusted RR 1.93, 95% CI 1.70 to 2.20).
How did the researchers interpret the results?
The researchers said that aspirin use that begins or is maintained after a diagnosis of colon cancer is associated with a lower risk of overall mortality. They added that aspirin may have an important role as an “adjuvant” cancer treatment, which is one given in addition to the main treatment.
“Our findings could have profound clinical implications,” said Dr Gerrit-Jan Liefers, the study’s lead author.
The findings of this large observational study are noteworthy but do not prove that aspirin is an effective treatment for bowel cancer or that it improves disease survival rates. One important limitation is the likelihood that many of the patients in the study were taking aspirin as a treatment for heart disease and stroke, rather than for bowel cancer. This could make the results less reliable as it is hard to separate the influence these conditions may have had on the health and survival of participants, making it difficult to isolate the influence aspirin may have had.
There are some further limitations:
- Researchers only looked at overall death rates for this group of patients (not death specifically due to cancer), so we do not know if the participants died of bowel cancer or other causes.
- Aspirin use was defined according to prescriptions for the drug. However, given that the drug is inexpensive, people may have used aspirin bought over the counter instead, and this may have distorted data on aspirin use.
- Patients who are prescribed a drug may not take it regularly, correctly or at all. Some participants considered to be aspirin users may not have been taking aspirin.
- Aspirin can cause unpleasant side effects, such as stomach pain or bleeds. Patients with worse bowel cancer may have been more likely to discontinue their aspirin use. They may also have been more likely to die.
There is a great deal of interest and research in the potential benefits of the simple aspirin pill. While this study is of interest, its design means that there may be many possible reasons for its results. A large randomised controlled trial would be a better way to assess whether aspirin is effective and safe as a treatment for bowel cancer.