Aspirin, which has already been shown to cut the risk for heart attacks, also appears to reduce the chances that women will be stricken by breast cancer, researchers reported yesterday.

A study involving 2,884 women found that those who took aspirin on a regular basis were about 28 percent less likely to develop breast cancer than those who never used the popular painkiller.

The findings are the latest in a series of studies that have indicated aspirin may do far more than relieve headaches, backaches and fevers. In addition to reducing the risk for heart attacks, several studies indicate it may cut the risk for various cancers, including breast cancer.

But scientists have remained uncertain whether aspirin reduces the chances of getting breast cancer because the level of protection appeared to be small and some studies have failed to find any effect, raising questions about whether the association was real.

The new study was designed to avoid some of the shortcomings of earlier research. It for the first time examined whether aspirin reduced the risk for particular types of breast cancer and found that, in fact, the protection appeared to apply only to cancers fueled by the hormone estrogen -- the most common form. Aspirin may interfere with estrogen's activity in the body.

The study also tried to tease out whether other types of commonly used painkillers had similar effects. It found that ibuprofen also appeared to reduce the risk, although the effect was much smaller, and that Tylenol (acetaminophen) had no apparent preventative effect.

"That's the new part that our paper adds to the literature," said Mary Beth Terry, an assistant professor of epidemiology at the Mailman School of Public Health at Columbia University, who led the study published in today's issue of the Journal of the American Medical Association.

Despite the results, Terry and other researchers said additional studies are needed to confirm the findings before considering recommending that women take aspirin specifically to reduce their risk for breast cancer. Aspirin can cause ulcers and increase the risk of dangerous bleeding.

"I would wait," Terry said in a telephone interview. "I would feel safer if other papers replicated these findings."

The findings do suggest, however, that women who take aspirin to cut their risk for heart attacks may be getting an additional benefit, Terry said.

Other experts agreed.

"Unfortunately, all the answers are not available and current information is insufficient to make any definite recommendations to patients," wrote Raymond N. DuBois of Vanderbilt University in an accompanying editorial.

For the study, researchers interviewed 1,442 women who had breast cancer and an equal number of similar women who did not.

Women who had used any anti-inflammatory painkiller, such as aspirin, at least once a week for at least six months, were about 20 percent less likely to develop breast cancer compared with women who had never taken aspirin. The greatest protection appeared to be among women who took aspirin most frequently -- at least seven tablets a week.

The findings suggest that aspirin, either alone or combined with other drugs, may provide a means for women to reduce their risk for breast cancer, the researchers said.

"Our data . . . bolster the case for the use of aspirin and [non-steroidal anti-inflammatory drugs] as chemopreventive agents against breast cancer," the researchers wrote.