THURSDAY, May 1 (HealthDay News) -- Women who take an aspirin each day may reduce their risk of developing the most common type of breast cancer by 16 percent, according to the results of a large study.

Estrogen receptor-positive breast cancer accounts for some 75 percent of all breast cancers, experts say. While aspirin reduced the risk of this form of breast malignancy, other painkillers did not, the U.S. team found.

"Many studies have looked at the relationship between nonsteroidal anti-inflammatory drugs (NSAIDs) and cancer, and the results have been all over the board," said lead researcher Gretchen Gierach, a cancer prevention fellow at the U.S. National Cancer Institute. "We want to further examine the question to see if we can add some clarity, since studies have looked at NSAIDs but haven't broken them down by type of NSAID."

The report is published in the April 30 online edition of Breast Cancer Research.

In the study, Gierach's team collected data on more than 127,000 women aged 51 to 72 with no history of cancer. All had participated in the U.S. National Institutes of Health-AARP Diet and Health Study. That study was designed to look at diet, health-related behaviors, and the risk for cancer.

Gierach noted that aspirin does has different biological effects compared to other NSAIDs.

Aspirin is one of many NSAIDs but unlike other NSAIDs it has irreversible effects on cyclooxygenase (COX) enzymes. For this reason, the researchers looked at the differences in cancer risk based on whether women took aspirin or other NSAIDs.

"Among women who reported taking aspirin on a daily basis there was a modest reduction in estrogen receptor-positive breast cancer," Gierach said.

Overall, NSAIDs did not affect the total risk of breast cancer. However, the daily use of aspirin was associated with a 16 percent reduction in the risk for estrogen receptor-positive breast tumors.

There was no link between daily aspirin and the incidence of estrogen receptor-negative breast cancer, the researchers report.

The finding could have important implications for cancer prevention, Gierach says, but a lot more work is needed to see if the effect is real. Moreover, she believes that it is still too early to recommend that women start taking aspirin to prevent breast malignancy.

"This is an exciting implication, if it's true," Gierach said. "But we need further clarity from other studies."

One expert noted that chronic aspirin use can have serious consequences and should not be used for cancer prevention.

"The American Cancer Society does not recommend using aspirin for cancer prevention because aspirin can cause serious gastrointestinal bleeding," said Eric J. Jacobs, Strategic Director of Pharmacoepidemiology in the department of epidemiology and surveillance research at the American Cancer Society.

Whether or not you should use aspirin for disease prevention is a question that should be discussed with your doctor, who can take your medical history into account, Jacobs said. "This decision should be based on balancing the proven benefits of aspirin in preventing heart disease against the proven risks of serious gastrointestinal bleeding," he said.

Another expert was intrigued by the findings.

"This theory has been around for many years," said Barbara Brenner, executive director of Breast Cancer Action. "If this works, it is a very exciting development for a lot of people who are thinking about how we can control not only cancer, but the price of cancer drugs."

The finding is confirming what many people have thought for a long time, Brenner added. But she stressed that aspirin would not be "a cure-all, it's only reducing the risk of estrogen positive-breast cancer."

Like the other experts, Brenner doesn't advise women to start taking aspirin to prevent breast cancer. "There are risks with aspirin, and there are people for whom aspirin is not indicated," she said. "But they might want to talk to their doctors about this study and whether aspirin is appropriate for them."

More information

For more information on breast cancer, visit the U.S. National Cancer Institute.