Painkillers such as Aspirin and ibuprofen may help reduce the risk of some breast cancers, but it's too soon to suggest taking the pills as a prevention strategy, according to a Canadian researcher who led the study.

Dr. Mahyar Etminan, a professor of medicine at the University of British Columbia and his colleagues at UBC and the University of Santiago de Compostela in Spain, analyzed data from 38 observational studies involving more than 2.7 million women to see whether anti-inflammatory drugs reduced the risk of breast cancer.

It's thought that inflammation may be a risk factor in cancer, Etminan said. Previous studies have shown conflicting results on the value of non-steroidal anti-inflammatory drugs (NSAIDS) in reducing the risk of developing breast cancer, but by combining the results, reviewers aim to spot trends that individual studies may miss.

In Tuesday's online issue of the Journal of the National Cancer Institute, Etminan's team concluded that women who took any kind of NSAIDS regularly had a 12 per cent relative reduction in risk of developing breast cancer compared with those who didn't take the drugs.

In a separate analysis, those who took ibuprofen had a 21 per cent relative risk reduction, while those who took ASA showed a 12 per cent relative reduction, the researchers found.

Why does reducing inflammation help?

"The results are encouraging and may help us better understand the importance of role of inflammation in the pathology of the disease," Etminan said. "However, we don't recommend the routine use of NSAIDs for breast cancer prevention until large randomized trials confirm these findings. Results from an ongoing trial will be available in 2009."

Regular use of painkillers may cause serious side-effects such as ulcers and increased risk of stroke, so the potential benefits in terms of cancer risks would have to be weighed against the risk after the randomized trial is completed.

NSAIDS work by blocking two proteins that promote inflammation in the body. The proteins are also thought to drive the growth of tumours in three ways: disrupting how cells die, promoting blood vessels that fuel tumours, and affecting how the immune system responds when it detects cancer.

"This meta-analysis provides evidence that NSAID use is associated with reduced risk for breast cancer," the study's authors concluded. "Future research should include careful evaluation of the biologic mechanisms involved in the relationship between NSAIDs and breast cancer."

The review is limited in that participants are asked to remember what medications they took, and it's possible the researchers did not adjust for all factors linked with the reduced risk, such as healthier behaviour among those who took the pills.

In a journal editorial accompanying the study, Dr. Scott Lippman of the University of Texas M.D. Anderson Cancer Center in Houston pointed out that a woman's response to each NSAID may depend on her menopausal status and how hormone receptors are expressed in breast cells — factors that may also explain why observational studies have turned up conflicting results.

There are also other ways for women to reduce their risk of breast cancer by reducing inflammation, said Dr. Hal Gunn, head of Inspire Health, a government-funded holistic cancer care centre in Vancouver.

"We don't need to take antinflammatories to reduce inflammation in our body," Gunn said in an interview. "There are many natural ways that we can do that."

These include eating more fruits and vegetables, taking omega-3 fatty acids and vitamin D, eating the spice turmeric, drinking green tea, and avoiding stress, cigarettes and trans fat, Gunn said.