Regular use of low-dose aspirin may lower breast cancer risk

A new study found that women who take low-dose or baby aspirin at least three times a week have a 20% lower risk of developing HR-positive/HER2-negative breast cancer, which is the most common breast cancer subtype. This is the finding of a study published online May 1 in Breast Cancer Research.

The study assessed the potential risk of breast cancer (overall and by subtype) according to use of aspirin and other non-steroidal anti-inflammatory medications (NSAIDs) in female public school professionals in California.

The team of researchers chose to focus on low-dose aspirin, because not only is it inexpensive and readily available as a potential means of prevention, but because there are a lot of people already taking it for prevention of other diseases such as heart disease and colon cancer.

Led by City of Hope’s Leslie Bernstein, PhD, the study used data from more than 57,000 women who were part of the California Teachers Study (CTS) and is the first to suggest that the reduction in risk is associated with low-dose aspirin.

Bernstein, professor and director of the Division of Biomarkers of Early Detection and Prevention at City of Hope, an independent research and treatment center in Duarte, Calif., says that one reason for the finding may be that aspirin can lower inflammation.

“Simple things like obesity or inflammatory conditions are a risk factor for breast cancer, so this may be one reason it could help," she says.

Bernstein and her colleagues saw an overall 16% 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% of estrogen or progesterone receptor positive, HER2 negative breast cancer.

“The study found an interesting protective association between low-dose aspirin and breast cancer,” according to lead author Christina A. Clarke, PhD, MPH, from the Cancer Prevention Institute of California. “We did not, by and large, find associations with other pain medications like ibuprofen and acetaminophen. We also did not find associations with regular aspirin since this type of medication is taken sporadically for headaches or other pain, and not daily for prevention of cardiovascular disease.”

The CTS cohort was established in 1995 to 1996 when 133,479 active and retired female teachers, administrators and other public school professionals were recruited through the California State Teachers Retirement System. Participants completed a baseline questionnaire that collected information on family history of cancer and other conditions, menstrual and reproductive history, self-reported weight and height, living environment, diet, alcohol and tobacco use, physical activity history, and frequency and duration of prior use of certain medications, including aspirin (but without detail on aspirin dose).

In 2005 to 2006, 57,164 participants completed a 10-year follow-up questionnaire, which collected updated information on frequency of current use of aspirin, low-dose aspirin and other pain-relieving medications, weight, alcohol use, menopausal status, use of hormone therapy (HT), and physical activity. In the ensuing years through 2012, 1,457 of these participants developed invasive breast cancer.

CTS participants are followed annually for changes of address, cancer diagnoses, hospitalizations, outpatient surgeries, emergency room visits and death. The CTS is overseen by the Institutional Review Boards of the Cancer Prevention Institute of California, the California Health and Human Services Agency, the University of California, Irvine, the University of Southern California, and the City of Hope.

Now that there is some data separating low-dose from higher-dose aspirin, more detailed research can be undertaken to understand the full value of low-dose aspirin for breast cancer prevention, Clarke says.

Since the writing of this study, Clarke has taken a position at GRAIL, Inc., Menlo Park, Calif.