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A new international study involving Canadian researchers is providing some of the most compelling evidence to date that anti-inflammatory drugs such as Aspirin and Advil may reduce a woman's risk of developing breast cancer.

Researchers reviewed 38 studies that involved a total of 2.7 million women from five countries and found that those who regularly took non-steroidal anti-inflammatory drugs (NSAIDs) had a lower incidence of breast cancer.

Past research has indicated there may be a link between the anti-inflammatory drugs and a reduced risk of breast cancer, but some of the results were inconsistent. The new study, being published in the Journal of the National Cancer Institute, is the largest review ever conducted of these studies and provides strong evidence of a relationship between the drugs, whose generic names are acetylsalicylic acid and ibuprofen, and a reduced breast-cancer risk.

"It is encouraging and we should definitely look into this further," said Mahyar Etminan, one of the study's authors and a scientist at the Centre for Clinical Epidemiology and Evaluation at Vancouver Coastal Health. The study was a joint effort by VCH, the University of British Columbia and the Universidade de Santiago de Compostela, in Spain.

NSAIDs are typically used to treat pain, fever, arthritis and other problems related to inflammation.

Dr. Etminan said the research is still too preliminary for physicians to start prescribing the drugs to women to ward off the disease. Prolonged use of these medications can cause serious side effects such as gastrointestinal bleeding. But the findings could eventually lead to new prevention options, she said.

In the review, researchers found that women who took any kind of NSAIDs on a regular basis had a 12-per-cent relative reduction in the risk of developing breast cancer compared with those who didn't take the drugs.

For women who took Aspirin, the reduction was slightly greater, at 13 per cent, while those who took Advil had a 21-per-cent reduction in their breast-cancer risk.

It's unclear exactly how or why NSAIDs may reduce the overall risk of developing breast cancer, but some research has pointed to the possibility that they may block an enzyme, cyclooxygenase, which plays a role in the development of cancer.

But Dr. Etminan said the study is an important step toward understanding how inflammation is linked to an elevated risk of cancer, and whether the drugs can one day be used as a preventive therapy in combination with other treatments.

"If ... this drug indeed does lower the risk of breast cancer, again, it could be used as an adjunct with hormone therapy. Or in conjunction with chemotherapy. It definitely would have its place as a preventive measure," said Dr. Etminan, who is also a professor of medicine at the University of British Columbia.

More research must be conducted in order to determine whether it would be effective and feasible to prescribe NSAIDs to women on a regular basis in order to guard against breast cancer, she said.

Right now, researchers in Britain are involved in a large randomized trial that could provide more definitive answers to those questions and lead to new treatment developments, Dr. Etminan said.

"I think that the results of that study would shed light into whether we actually want to prescribe these drugs routinely to prevent [breast cancer]," she said.