Daily Aspirin Use Failed to Improve Breast Cancer Outcomes, Led to ‘Slightly Worse Survival’ Than Placebo

A large study of women with HER2-negative breast cancer showed that daily aspirin use had no effect on breast cancer outcomes.

While prior research has suggested that daily aspirin use may have anti-tumor effects, a recent study found no difference in invasive disease-free survival between patients with HER2-negative breast cancer who took a full-strength aspirin daily and those who did not.

“Although inflammation may still play a key role in cancer, it’s also important to remember that aspirin may have different effects in other cancers, such as colon, or in a different setting, such as primary versus secondary prevention,” study author Dr. Wendy Y. Chen, a medical oncologist at the Dana-Farber Cancer Institute in Boston, explained while presenting the data.

The study, which was presented at the February ASCO Plenary Series, included more than 3,000 patients under the age of 70 with HER2-negative breast cancer who were randomly split into two groups: one half which took 300 mg of aspirin every day, while the others were given a placebo.

The main goal of the study was to compare invasive disease-free survival, which means that patients were still alive without breast cancer recurrence or secondary breast cancer. Other goals were overall survival (time patients were alive), cardiovascular disease, side effects and adherence to the aspirin or placebo protocol.

“Aspirin users had a slightly worse survival than placebo arm,” Chen said.

Findings showed that the aspirin users actually had a higher amount of disease events than the placebo group (111 compared to 90, respectively), though the difference was not statistically significant, and the types of events were relatively balanced between the two groups, the researchers explained.

There was also a similar amount of severe adverse events between each of the arms.

“The incidence of grade 3 or higher (side effects) was similar for aspirin versus placebo, focusing specifically on grade 4 events, in the aspirin (group), you will note that there were no grade 4 cardiac, hematologic or gastrointestinal events due to aspirin,” Chen said.

However, another expert that was involved in the ASCO Plenary Series noted that the characteristics of the patient population may play a role in the outcomes that were observed.

“From these data, we can conclude that this high event rate amongst a postmenopausal, overweight population who had hormone-receptor positive, high-risk disease was to be expected. And this is exactly the group that one would want to try to intervene upon, because we’d expect this group to have high levels of inflammation,” said Dr. Angela DeMichele, co-leader of the Breast Cancer Research Program and director of the Breast Cancer Clinical Trials Unit at Penn Medicine’s Abramson Cancer Center.

Additionally, DeMichele pointed out that about 44% of patients dropped out in the early stages of the trial, though the reasons why were not made known — and could be interesting to consider. Those who stayed on the trial did so because they were willing and comfortable to take aspirin daily. Study participants reported on whether or not they were adherent to taking their aspirin or placebo daily, and DeMichele noted, “self-report can be notorious for over-estimates of adherence.”

Despite potential reasoning for the poorer aspirin outcomes, this was not the first study to show that aspirin use may not improve cancer-related outcomes. In 2018, findings from the Aspirin in Reducing Events in Elderly (ASPREE) trial were published, and they showed worse outcomes for elderly patients (over the age of 70) who took daily aspirin.

“Aspirin users (in the ASPREE trial) were found to have an increased risk of death – that was mainly driven by increased risk of cancer deaths. Of note, 19% had a prior history of cancer,” Chen said.

The United States Preventive Services Task Force (USPSTF) currently recommends daily aspirin for the prevention of colorectal cancer in individuals between the age of 50 and 59 who have a 10-year cardiovascular risk of 10% or higher. However, the jury is still out when it comes to the risks and benefits of aspirin use in older adults.

“So what we can take away from this study (presented at the ASCO Plenary Series) for patients and providers is that at this time, aspirin should not be used simply to prevent breast cancer recurrence. For those situations in which there are other options, decisions about aspirin use for other indications should definitely include an individualized risk/benefit discussion between physician and patient,” DeMichele said.

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