‘Aspirin can lower risk of breast cancer’ – No mention that this was an observational study

City of Hope researchers find regular use of aspirin can lower risk of breast cancer for women

Our Review Summary

breast cancerThe release focuses on a recent paper published in the journal Breast Cancer Research, which addresses breast cancer risk and regular use of aspirin in low doses. While the release states that low doses of aspirin “reduces the risk of breast cancer in women,” there are problems with how the information is presented. Specifically, it’s impossible to know whether the aspirin affected breast cancer risk based on this study. That’s because this was an observational study — meaning that it could detect a correlation between aspirin use and breast cancer, but not whether the use of aspirin was actually responsible for lower rates of breast cancer. That’s a key distinction.


Why This Matters

Breast cancer is the second most common type of cancer among women in the United States and is diagnosed in hundreds of thousands of women each year. That means many thousands — if not millions — of women and their loved ones are on the lookout for things they can do to reduce their risk of developing breast cancer. Telling the public that aspirin reduces cancer risk has the potential to influence the daily decisions of those women, which is problematic when the relevant study is unable to make that determination. What’s more, daily aspirin use can cause or exacerbate other health problems, which this release does not address at all.


Does the news release adequately discuss the costs of the intervention?


The release notes, near the bottom, that low-dose aspirin is inexpensive. That’s enough to earn it a satisfactory rating here since low-dose aspirin is indeed inexpensive. Costs for a bottle of 300 tablets currently range from $3.47 to $12.49 according to an online search.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

The release shares relative risk reduction numbers only, not the actual numbers of people who reduced their risk of breast cancer by taking aspirin.

The release notes that the research team “saw an overall 16 percent lower risk of breast cancer in women who reported using low-dose aspirin at least three times per week. Such regular use of low-dose aspirin reduced the risk by 20 percent of estrogen or progesterone receptor positive, HER2 negative breast cancer, which is the most common breast cancer subtype.” That’s fine. The problem is that, as noted above, this was an observational study, not a clinical study designed to determine whether a specific intervention (i.e., aspirin use) was responsible for reducing cancer risk.

Does the news release adequately explain/quantify the harms of the intervention?

Not Satisfactory

The release doesn’t address potential harms at all — and regular use of low-dose aspirin isn’t for everyone. As the Mayo Clinic notes, people with some medical conditions are at greater risk of complications associated with daily aspirin therapy.

It’s well known that daily aspirin use can cause serious gastrointestinal bleeding in some people, which is why experts recommend a careful risk-benefit calculation even where benefits are more conclusively established — as in the prevention of heart disease. It’s irresponsible not to mention those risks in the context of a speculative benefit such as breast cancer prevention.

Does the news release seem to grasp the quality of the evidence?

Not Satisfactory

Observational studies, like this one, can only identify correlations. In this case, the researchers found that women who took low doses of aspirin on a regular basis were less likely to get breast cancer. However, these studies can’t prove a causal relationship — i.e., that the action (taking aspirin) caused the result (reduced risk of breast cancer). The release does not make that clear, which is important. The release also doesn’t address whether other factors — such as age, weight, lifestyle choices, etc. — may have contributed to the difference in breast cancer rates. The release notes that all of this information was collected, but doesn’t explain how (or whether) it was used by the research team.

Another important omission in the release was that more than 4,000 women who had developed breast cancer before the 10-year follow-up were excluded from the study. This should have been mentioned as a limitation. We wonder how these women who were excluded differed in their low-dose aspirin intake from those who developed breast cancer later on.

Does the news release commit disease-mongering?


No disease mongering here. The release mentions that HER2 negative is the most common type of breast cancer.

Does the news release identify funding sources & disclose conflicts of interest?


The release clearly identifies the sources of funding. It does not address conflicts of interest, but there do not appear to be any relevant conflicts of interest. Still, the release would have been stronger if it had stated that explicitly.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

There are a host of things that women can do to reduce their risk of breast cancer. However, none of these things are mutually exclusive. One can be physically active and limit alcohol intake, for example. None of these other ways to reduce breast cancer risk are mentioned.

Does the news release establish the availability of the treatment/test/product/procedure?


The release explicitly states that low-dose aspirin is “readily available” and that’s widely known to be the case.

Does the news release establish the true novelty of the approach?


The release claimed novelty head on, noting that the study “is the first to suggest that the reduction in risk occurs for low-dose aspirin” and “This study differed from other studies that have looked at aspirin and cancer risk because it focused on the dose levels of the aspirin women had taken and tracked the frequency of the use of low-dose aspirin as opposed to regular aspirin. It was also able to look in detail at subtypes of breast cancer.”

That may be a bit of hair-splitting. Aspirin (perhaps at different dosages) has been studied as a potential preventative in breast cancer previously. The American Cancer Society noted on its website in 2015 that “None of these studies are randomized trials, the most reliable type of study, where people are randomly assigned to take either aspirin or a placebo pill.”

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?


The release doesn’t rely on overtly sensational terms like “breakthrough” or “cure.”

We’ve already commented on the inappropriate causal language such as found in the headline which states “regular use of aspirin can lower risk of breast cancer for women” and in the first sentence which claims the study “found that the use of low-dose aspirin (81mg) reduces the risk of breast cancer in women who are part of the California’s Teacher’s Study.” The study found a correlation between those two things, but that’s all.

Total Score: 6 of 10 Satisfactory


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