The researchers followed 440 breast cancer survivors -- most of them past menopause and overweight or obese -- who were diagnosed between 1987 and 2011. The women had estrogen receptor-positive breast cancer, which requires the hormone estrogen to grow.
Over the seven-year follow-up, taking the pain medications was linked to a difference in recurrence: "Twelve percent of those not taking NSAIDs had a recurrence, but 6 percent of those taking the drugs did," said study author Linda deGraffenried, an associate professor of nutritional sciences at the University of Texas in Austin.
Of the 440 women, 159 used painkillers and 281 did not. Most of those using painkillers took aspirin, deGraffenried said, while some took other types of NSAIDs, such as Motrin or Aleve.
The average body mass index (BMI) of the women was about 31. BMI is a measurement based on height and weight. A BMI of 30 and higher is termed obese; a BMI of 25 to 29.5 is considered overweight. At the time of diagnosis, the women were about age 55 to 60.
If the cancer did recur, it took longer in those who took painkillers: 6.5 years compared to about 4.2 years for the nonusers, the investigators found.
How could the painkillers, which the women took for arthritis and other problems, help? The key may be the anti-inflammatory properties of the medicines, deGraffenried said.
Researchers know that obese women who develop estrogen-positive cancers do worse when they are given hormone therapy known as aromatase inhibitors. "One of the key reasons that obese women do worse on hormone therapy is because of inflammation induced by obesity," deGraffenried said. Reducing the inflammation with aspirin and other NSAIDs, she explained, may improve how well the hormone therapies work.
However, deGraffenried noted, it's too soon to recommend taking NSAIDs for reducing either breast cancer recurrence or development. And while the researchers found an association between NSAID use and a reduced risk of breast cancer recurrence, the study was not designed to prove cause and effect.
Also, painkillers have side effects, she added, such as a risk of gastrointestinal bleeding.
If future research bears out the latest findings, deGraffenried said, giving women with estrogen receptor-positive breast cancer a daily NSAID may reduce or delay the return of the breast cancer, and possibly spare them from needing additional treatments.
The concept makes sense, said Leslie Bernstein, director of the division of cancer etiology at the Beckman Research Institute of the City of Hope Cancer Center in Duarte, Calif. Bernstein is a longtime breast cancer researcher.
"We think of obesity as an inflammatory condition, and women who are obese have a higher risk of recurrence," she said. (In her own research, she has found that higher risk occurs in white, but not black, women.) It does make sense, she said, that aspirin would reduce inflammation and thus the risk of recurrence.
However, the study has some limitations, Bernstein noted. It relies on chart reviews, for instance, not direct interviews with the women. It would also have been valuable to look at aspirin alone, she added, rather than a variety of NSAIDs.
Bernstein agreed more work should be done, including clinical trials to focus on aspirin. If the research continues to bear out, she said, a recommendation to take a daily aspirin might help reduce recurrence of breast cancer.
This preventive measure might be adhered to better than other advice to minimize breast cancer risk, such as increasing physical activity, Bernstein added.
"You can't get all women to exercise," she said, "but you can get them to take an aspirin every day."
The study is published in the Aug. 15 issue of the journal Cancer Research. The research was funded by the U.S. Department of Defense, the U.S. National Cancer Institute and the Breast Cancer Research Program of the Congressionally Directed Medical Research Programs.
To learn more about cancer recurrence, visit the American Cancer Society.