Women who take aspirin regularly might have a significantly lower risk of developing breast cancer -- more evidence that the century-old "wonder drug" can help prevent a wide range of deadly diseases.
Researchers at Columbia University found that women who took aspirin at least once a week for six months or longer had a 20 percent lower risk of breast cancer than those who took none.
The risk decreased even more markedly for frequent users: Women who took at least seven tablets a week were 28 percent less likely to get the disease.
The researchers did not determine how long women had to use aspirin to receive its protective effect, but found that the benefit was stronger among current or recent users.
Previous studies have identified an association between aspirin use and reduced breast cancer risk. But the latest report, in today's Journal of the American Medical Association, specifically ties aspirin's apparent protection to the most common type of breast cancer -- which relies on estrogen to grow.
Experts say that up to three-quarters of breast cancer cases involve these so-called "hormone receptor-positive" tumors, which occur primarily in post-menopausal women.
"It gets us one step closer to concluding that this is a real association and [saying] that we're going to recommend this" for at-risk women, said Mary Beth Terry, assistant professor of epidemiology at Columbia's Mailman School of Public Health and the study's lead author.
Modern aspirin was born in 1897, when Bayer AG chemist Felix Hoffman, hoping to treat his father's painful rheumatoid arthritis, resurrected a long-ignored formula for acetylsalicylic acid, the drug's active ingredient. That compound's precursor -- derived from the juice in willow tree bark -- was used as a pain reliever by doctors dating back to ancient Greece.
Bayer patented the drug under the trade name Aspirin in 1899, and it became phenomenally successful. But over the years, its use -- more than 80 million tablets are consumed in the United States every day -- has expanded far beyond aches and pains into the realm of preventive medicine.
By thinning the blood and helping prevent clots, aspirin can significantly reduce the risk of heart attacks. It also has shown promise in protecting against several types of cancer, including colon, esophageal and stomach cancer.
To that end, some have begun to view aspirin -- which is readily available and inexpensive -- as a sort of wonder drug.
"I try to be quite conservative in my estimation of things, but I have to start looking at it the same way," said Dr. Ernest Hawk, chief of gastrointestinal cancer prevention at the National Cancer Institute, who was not involved in the study. "It seems to have a lot of [beneficial] effects."
New research aside, doctors warn that aspirin can have serious side effects, too. It can cause gastrointestinal bleeding, ulcers and kidney problems and might increase the risk of certain types of stroke.
"It's never an easy decision in prevention because you're always weighing risks and benefits, and that's always determined on an individual basis," said Hawk.
The researchers stress that the study data aren't conclusive enough to sustain a blanket recommendation that all women with a family history of breast disease take aspirin.
"I think the evidence isn't far along enough for that recommendation," said Dr. Alfred I. Neugut, a Columbia epidemiologist and study author who serves as co-director of the cancer prevention program at NewYork-Presbyterian Hospital.
The women in the study -- one group had cancer and the other was cancer-free -- were interviewed in 1996 and 1997 as part of the Long Island Breast Cancer Study Project. They were predominantly white and ranged in age from 20 to 98.
Researchers asked them to report their intake of aspirin, ibuprofen and acetaminophen, including how often they took the drugs and for how long. Dosage was not considered.
The researchers found the association between aspirin use and reduced cancer risk was greatest among the most frequent users -- and among those who were taking the drug or who took it in the previous five years.
The association between ibuprofen and decreased risk of breast cancer was less clear, they said. There was no association at all with acetaminophen use.
That made sense, said lead author Terry, given what scientists know about the way aspirin and other so-called nonsteroidal anti-inflammatory drugs affect the body. These drugs block production of prostaglandins -- hormone-like substances that control blood pressure, muscle contractions and inflammation. Prostaglandins are responsible, directly or indirectly, for a cascade of other biologic effects, including estrogen production.
"What we think is happening is that the aspirin is working in the pathway that's actually reducing the synthesis of estrogen," said Terry. "Estrogen and other hormones promote the growth of the cancers."
In an accompanying editorial in the medical journal, Dr. Raymond N. DuBois, director of cancer prevention at the Vanderbilt-Ingram Cancer Center in Nashville, Tenn., noted that more research is necessary to determine what dose of aspirin might provide the protective effect.
"Even though it's very commonly used for aches and pains, it can lead to some serious side effects, especially if you take it on a regular basis, as you would need to do to get protection against this sort of breast cancer," DuBois said. "We don't know the proper dose or regimen to provide the benefit."