Thursday May 1 2008
Of the NSAIDs, only aspirin was linked to a reduction in risk
“Aspirin a day helps reduce breast cancer risk” is the headline in the Daily Mirror today. The newspaper says that 75% of breast cancers are fuelled by the female hormone oestrogen and that a study found that “a daily dose of aspirin was linked to a 16% reduction in the risk of having this form of the disease”.
The US research that the newspaper story is based on is reliable, but needs careful interpretation. The study looked at aspirin, which is part of a group of drugs known as non-steroidal anti-inflammatory drugs (NSAIDs). The researchers are cautious in their conclusions suggesting that further research is needed, because the link with aspirin was only modest and did not appear to extend to all drugs in the group. Regular daily use of aspirin and NSAIDs also carry risks, notably irritation to the stomach lining and an increased risk of bleeding and ulceration. With the present level of evidence, some of which is conflicting, it seems inadvisable for women to start taking these drugs on a daily basis, purely in the hope that it will reduce their risk of breast cancer.
Where did the story come from?
Dr Gretchen Gierach from the National Cancer Institute and other colleagues from the US carried out this research. The study was supported by a research programme of the National Institute of Health. It was published in Breast Cancer Research a peer-reviewed medical journal.
What kind of scientific study was this?
This cross-sectional study looked at the questionnaire responses from a previous study and used these answers to relate the use of NSAIDs to the chance of developing breast cancer between 1993, when the original study started, and 2003.
The previous study was called the Diet and Health Study and was a prospective cohort study where 3.5 million members of the American Association of Retired Persons in six states and four cities in the US, aged 50 to 71 years, were sent a questionnaire for enrolment. Over 560,000 people completed and returned the questionnaire satisfactorily and of these, 136,408 women directly answered the second questionnaire a year or so later. It was from this potential group that the 127,383 women, now aged 51 to 72 years, with no history of cancer, were selected for this study.
The questionnaire the women were sent asked whether aspirin products or non-aspirin NSAIDs (such as ibuprofen or naproxen) had been used in the past 12 months. The researchers divided the usage into four categories: non-use, less than once per week, one to six times per week and once per day or more. The dose, duration and reason for use were not recorded. Alongside the age and reproductive history of the women, the researchers also asked for other details of the medical history. This included things such as history of high blood pressure, the number of mammograms carried out and details of the amount of vigorous physical activity undertaken. Information was also collected on the use of hormone replacement therapy and whether there was a strong family history of breast cancer.
The researchers looked at the links between NSAID use and breast cancer by entering the data into statistical models that could estimate the strength of any association and the statistical significance of any increased risks they found.
What were the results of the study?
The researchers found no statistically significant association between overall NSAIDs and total cases of breast cancer. When they tested the links by NSAID type, they found no statistically significant differences in risk for people who took aspirin daily compared with those who took no aspirin or other non-aspirin NSAIDs.
The chance of developing a particular type of breast cancer that is positive to oestrogen receptors, was significantly reduced by about 16% in people who took aspirin daily, but not for those that took other non-aspirin NSAIDS. Neither aspirin nor non-aspirin NSAIDs were associated with a risk of the type of breast cancer that is negative to oestrogen receptors.
What interpretations did the researchers draw from these results?
The researchers conclude that “breast cancer risk was not significantly associated with NSAID use, but daily aspirin use was associated with a modest reduction in oestrogen-receptor (ER)-positive breast cancer. Our results provide support for further evaluating relationships by NSAID type and breast cancer subtype.”
What does the NHS Knowledge Service make of this study?
The 16% reduction in risk is modest as the researchers suggest. The fact that the reduction in risk was shown for one subtype of breast cancer and for one dose of a single drug type – aspirin –suggests that further research is required.
The researchers point out other studies that have shown conflicting results, with the implication that it is too soon to be suggesting that researchers know whether taking or not taking aspirin could be a way of reducing risk of breast cancer. Additionally it should be noted that regular daily use of aspirin and NSAIDs does carry its own risk, notably irritation to the stomach lining and increased risk of bleeding and ulceration; elderly patients are often most sensitive to this. With the current level of evidence, it seems inadvisable for women to start taking these drugs on a daily basis purely in the hope that it will reduce their risk of breast cancer.
For an important disease such as this, which has such far reaching personal and public health implications, it appears yet more research is required.
Sir Muir Gray adds...
Aspirin is probably the greatest drug, and it is cheap.