New study linking pain relievers and breast cancer fails to convince experts

Research in recent years has consistently linked the use of aspirin and other anti-inflammatory pain relievers with a lower risk of colon cancer, but findings about the drugs' effect on breast-cancer risk have been very mixed with some studies suggesting that the pain relievers protect against breast cancer, while others have found no link.

Now a new study of California teachers has re-ignited that debate.

The study, is the first to suggest that long-term ibuprofen or aspirin use might actually raise the risk of breast cancer, but the lead author University of Southern California researcher Sarah Marshall, says they were expecting ibuprofen and aspirin to reduce the risk and admits there is no biological explanation for that surprising finding.

Alfred Neugut, a Columbia University scientist, who co-wrote a study published last year that linked the use of anti-inflammatory pain relievers to at least a 20% reduction in breast-cancer risk, says Marshall's ibuprofen finding is "totally at odds with every other paper" on the subject.

American Cancer Society scientist Michael Thun suggested in a statement on Tuesday that Marshall's findings of a higher breast-cancer risk in aspirin or ibuprofen users might be because of chance. He does however say it underscores concern about the potential toxicities from long-term regular use of these drugs.

Thun is the co-author of a study which came out in January that found no link between the pain relievers and breast-cancer risk.

Marshall's study analyzed data on 114,460 women in the ongoing California Teachers Study, the women were 22 to 85 years old and free of breast cancer when they enrolled in the study a decade ago. At that time, they told researchers how often and how long they had used aspirin and ibuprofen.

From 1995 to 2001, 2,391 of the women were diagnosed with breast cancer and when regular aspirin and ibuprofen use were lumped together, researchers found no link to breast-cancer risk.

But when the scientists broke their findings down by pain reliever or type of breast cancer, they found that women who took ibuprofen daily for at least five years were about 50% more likely to be diagnosed with breast cancer than those who did not take the drug regularly, and women who took aspirin daily for at least five years were 80% more likely to develop breast cancers that were not sensitive to the hormones estrogen or progesterone than women who were not regular users of aspirin.

Long-term daily aspirin users were 20% less likely to develop the more common type of breast tumor, one that is sensitive to hormones. But, the scientists say the difference was so small it might have been a result of chance.

Marshall does caution that no one should stop or start taking a pain reliever because of her study's findings, she does say however that she is fairly convinced from the studies that aspirin and ibuprofen are not reducing breast cancer.

The study is published in the Journal of the National Cancer Institute.