Wednesday February 17 2010
“Aspirin may halve the risk of death from breast cancer in women who have had early treatment for the disease”, The Independent reported.
This news story is based on research that looked at aspirin use in over 4,000 nurses who had been treated for breast cancer. The study found that there was an association between frequent use of aspirin and a decreased risk of recurrence of cancer and breast cancer-related death.
This is a preliminary study and cannot determine whether aspirin directly caused the difference in cancer recurrence and survival. Further research is needed. Most useful would be a randomised controlled trial comparing breast cancer patients taking aspirin with patients who are not.
Aspirin is not without risks. Regular use can increase the risk of stomach irritation and bleeding, particularly in the elderly and in people who are taking medical treatments that increase their risk of bleeding. Importantly, people undergoing chemotherapy may be more susceptible to bleeding, so may be advised not to use aspirin. Individuals are advised to approach their GP with further questions.
Where did the story come from?
This research was carried out by Professor Michelle Holmes and colleagues from the Brigham and Women’s Hospital and Harvard Medical School, US. The study was funded by grants from the National Institutes of Health. The paper was published in the peer-reviewed Journal of Clinical Oncology. The research was covered accurately by The Independent.
What kind of research was this?
This prospective observational study investigated whether there is an association between aspirin use and the recurrence of breast cancer and deaths from the disease.
One of the effects of aspirin is to reduce inflammation in the body, and the researchers were interested in this property. A number of previous studies have suggested that these anti-inflammatory actions may protect against various cancer processes. The researchers suggest that cancer cells have an increased immune response compared to healthy cells. They say that, in cell culture studies in the laboratory, aspirin has been shown to reduce the amount of inflammatory chemicals released by cancer cells and to inhibit cancer growth. They wanted to see whether there was any difference in survival and recurrence of breast cancer in women who had breast cancer and who had routinely taken aspirin, compared to those who had not.
This type of study was designed to look for associations between aspirin use and breast cancer outcome. It cannot determine whether aspirin directly caused any increase in survival or reduction in cancer recurrence.
What did the research involve?
This research used data from the US Nurses’ Health Study, which has followed 121,700 female registered nurses, aged between 20 and 55, since 1976. Every two years the nurses answered a mailed questionnaire on cancer and cardiovascular risk factors. For any report of breast cancer, the participants gave permission for a doctor to review their medical records.
The nurses’ use of aspirin was first assessed by questionnaire in 1980 and then every two years afterwards. Aspirin use was categorised as ‘never’, ‘past use after breast cancer diagnosis that subsequently stopped’ and ‘current use’. The frequency of use was classified as once a week, two to five times a week, or six to seven times a week. Assessments of aspirin use in the first 12 months after diagnosis were not included as aspirin use is discouraged during chemotherapy.
The researchers asked the women who used aspirin a series of questions as to why they were taking the aspirin, such as for heart disease prevention, muscle or joint pain, headache and menstrual cramps.
Deaths were reported by the family or the post office. The reviewers ascertained the cause of death from death certificates.
When analysing the data, the researchers adjusted for how advanced the participants’ cancer was, their diet, physical activity, body mass index, weight change, reproductive factors and smoking. They also adjusted for the type of treatment that the participants had received, such as chemotherapy, radiotherapy or hormonal therapy.
In total, the study looked at the information from 4,164 participants, for whom aspirin use was assessed after breast cancer was diagnosed between 1980 and 2006.
What were the basic results?
Of the 4,164 participants diagnosed with breast cancer whose aspirin use had been assessed, there were 341 breast cancer deaths and 400 distant recurrences (including the breast cancer deaths).
Aspirin was associated with a lower risk of death from breast cancer. For women who took aspirin two to five days a week, there was a 71% lower risk of death (relative risk [RR] 0.29, 95% confidence interval (CI) 0.16 to 0.52) compared to individuals who had never taken aspirin. For women who currently took aspirin between six and seven days a week, risk was 64% lower (RR 0.36, 95% CI, 0.24 to 0.54). Past use and current use on one day a week was not related to a significant reduction in risk.
When the researchers examined just the data from the first aspirin assessment questionnaire (taken after breast cancer diagnosis), there was no association between a reduced risk of breast cancer death and aspirin use.
The relative risk of breast cancer recurrence was also lower for women who took aspirin two to five days a week or six to seven days a week (RR 0.40, 95% CI 0.24 to 0.65 and RR 0.57, 95% CI 0.39 to 0.82, respectively).
How did the researchers interpret the results?
The researchers conclude that using aspirin after breast cancer diagnosis was associated with a decreased risk of breast cancer-related death and recurrence.
They say that this is notable as previous analysis of data from the Nurses’ Health Study as a whole did not find an association between aspirin use and breast cancer incidence (the chance of developing breast cancer). They propose that further studies are needed including, ultimately, a randomised controlled trial of aspirin use after breast cancer diagnosis.
This preliminary study found an association between the frequency of aspirin use and the risk of recurrence of breast cancer and breast cancer-associated deaths.
The researchers highlight the following limitations of the study:
- The women’s aspirin intake, treatments and whether their cancer reoccurred were given by self-report. It is possible that participants may not have accurately recalled this information.
- The study only asked about the weekly frequency of aspirin use and did not ask about the daily dose of aspirin that participants took. This is likely to vary between individuals.
- The study population were all nurses who worked within the health system. It is possible that their health and lifestyle may differ from the general population.
- This type of study cannot determine whether aspirin caused the observed reduced risks. To better establish this, follow-up research should include a randomised controlled trial to compare the prognosis for people given a defined dose of aspirin after breast cancer treatment with people who did not take aspirin.
Importantly, aspirin is not without risks. Regular use of aspirin or other anti-inflammatory drugs, such as ibuprofen, can increase the risk of stomach irritation and bleeding, particularly in the elderly and in people who are taking other medical treatments that increase their risk of bleeding.
People undergoing chemotherapy are especially at risk as they may be more susceptible to bleeding (due to the effect of chemotherapy on platelet count) so may be advised not to use aspirin.