Aspirin Doesn't Prevent Breast Cancer

May 31, 2005 -- What a difference a year makes. A study released last May made national headlines with the finding that aspirin can reduce a woman's risk of breast cancer.aspirin can reduce a woman's risk of breast cancer. Now a new study shows little protective benefit and a possible increase in breast cancer among women who take aspirin or ibuprofen.

Researchers downplayed the potential risk but called the failure to find a protective benefit for the anti-inflammatory pain relievers disappointing.

"These drugs are not preventing breast cancer as earlier studies suggested that they might," Sarah F. Marshall of the University of Southern California, Los Angeles, tells WebMD. Mixed Findings for Daily Use

Marshall and colleagues analyzed data on more than 114,000 California women. None of the women had breast cancer when they entered the study, but nearly 2,400 were diagnosed with the disease between 1995 and 2001.

Their findings are reported in the June 1 issue of The Journal of the National Cancer Institute.

The researchers reported that taking aspirin or ibuprofen more than once a week but not every day neither increased nor decreased breast cancer risk. Other anti-inflammatory drugs, such as naproxen, were not studied.

Daily aspirin use for more than five years, however, was linked to a small increased risk for developing breast cancers called hormone receptor-negative tumors. Breast cancers are classified based on whether or not they grow in response to hormones, such as estrogen. Tumors that do not respond to hormones -- hormone receptor-negative -- are less common and harder to treat.

But the risk from daily aspirin use is small. The researchers say that among the nearly 2,400 women with breast cancer, seven excess cases of hormone receptor-negative cancer may be caused by long-term daily aspirin use. The study did not compare the risks of low-dose "baby" 81 milligram aspirin to the regular 325 milligram dose.

Small Risk With Ibuprofen

Daily ibuprofen use was also linked to an increase in breast cancer risk among women in the study. The risk was higher for women with tumors that had spread to other parts of the body.

But again the actual risk was small. The researchers estimated that 24 of the nearly 2,400 cases of breast cancer could be due to daily ibuprofen use.

Marshall says the findings should not discourage women who are taking a daily low-dose aspirin to lower their risk of heart disease.

"I would not advise women to take these drugs to prevent breast cancer," she says. "But women who are taking them for other good reasons should not stop because of this study."

Regular or daily use of acetaminophen, which is not an anti-inflammatory drug, had no effect on breast cancer risk.