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Study Suggests Link Between Low-Dose Aspirin and Lower Risk for Specific Type of Breast Cancer

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Many people take low-dose aspirin (also called baby aspirin) to reduce the risk of heart disease. A low dose of aspirin is 81 mg per day. Aspirin reduces inflammation and is also a weak aromatase inhibitor. Aromatase inhibitor medicines -- Arimidex, Aromasin, and Femara -- are used to treat hormone-receptor-positive breast cancer.

Earlier studies have suggested that people who regularly take low-dose aspirin may have a lower risk of breast and some other cancers. Still, these studies didn’t look at whether any possible risk reduction was linked to the characteristics of the breast cancer.

A preliminary study suggests that women who take low-dose aspirin 3 or more times per week have a lower risk of hormone-receptor-positive, HER2-negative breast cancer. Still, experts say that it’s too soon to recommend women start taking low-dose aspirin to reduce breast cancer risk.

The study was published online on May 1, 2017 by the journal Breast Cancer Research. Read “Regular and low-dose aspirin, other non-steroidal anti-inflammatory medications and prospective risk of HER2-defined breast cancer: the California Teachers Study.”

To do the study, researchers from the City of Hope analyzed information in questionnaires answered by women in the California Teachers Study. City of Hope is one of 47 National Cancer Institute-designated comprehensive cancer centers in the United States. The California Teachers Study was started in 1995 to study how the participants’ health behaviors affected their risk of breast and other cancers. More than 133,475 women are participating in the study.

The questionnaires asked about:

  • the women’s family history of cancer and other conditions
  • how often they took aspirin and other non-steroidal anti-inflammatory (NSAIDs) medicines, such as ibuprofen and acetaminophen
  • the women’s height and weight
  • the women’s menstrual and child-bearing history
  • living environment
  • diet
  • alcohol use
  • physical activity

From 2005 to 2006, 57,164 of the women in the study provided updated information on how often they took aspirin, low-dose aspirin, and other pain medicines, as well as their weight, alcohol use, menopausal status, physical activity, whether they used hormone replacement therapy after menopause, and any cancer diagnoses.

From the time they provided updated information to Dec. 31, 2012, 1,457 of the 57,164 women were diagnosed with breast cancer. Of these breast cancer diagnoses:

  • 68% were hormone-receptor-positive, HER2-negative
  • 8% were hormone-receptor-positive, HER2-positive
  • 3% were hormone-receptor-negative, HER2-positive
  • 9% were hormone-receptor-negative, HER-negative
  • 11% were missing information on hormone receptor or HER2 status

Low-dose aspirin was the NSAID the women in the study used most often:

  • 23% took at least three low-dose aspirin tablets per week
  • 18% took at least three ibuprofen tablets per week
  • 11% took at least three regular-dose aspirin (325 mg) per week

After analyzing the information, the researchers found that compared to women who didn’t regularly take NSAIDs:

  • women who took low-dose aspirin at least 3 times per week had a 16% lower risk of any type of breast cancer
  • women who took low-dose aspirin at least 3 times per week had a 20% lower risk of hormone-receptor-positive, HER2-negative breast cancer

"The study found an interesting protective association between low-dose aspirin and breast cancer," said lead author Christina Clarke, Ph.D., MPH, of the Cancer Prevention Institute of California. "We did not by and large find associations with the 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."

While the results of this study are promising, it’s important to remember that this is an observational study. Observational studies can’t determine cause and effect. They can only detect associations that can be studied in more detail.

“Patients should ask their doctor about taking aspirin for risk reduction,” said Brian Wojciechowski, M.D.,’s medical adviser. “Additionally, there are no known drug interactions between aromatase inhibitors and aspirin. It’s not known if aspirin would decrease the effectiveness of the aromatase inhibitor.”

More research, including randomized clinical trials, are needed before we understand how and if low-dose aspirin might be used to reduce breast cancer risk.

It’s also important to know that regularly taking NSAIDs, including low-dose aspirin, can cause side effects including stomach ulcers and bleeding.

Stay tuned to Research News for the latest information on low-dose aspirin and breast cancer risk.

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