A new study of California teachers fuels the debate about whether aspirin, ibuprofen or other, related pain relievers affect breast-cancer risk.
Although research has consistently linked use of aspirin and other anti-inflammatory pain relievers with a lower risk of colon cancer, findings about the drugs’ effect on breast-cancer risk have been mixed. Some suggest that the pain relievers protect against breast cancer, while others have found no link.
The latest study, out today in the Journal of the National Cancer Institute, is the first to suggest that long-term ibuprofen or aspirin use might actually raise the risk of breast cancer. But the lead author says there is no biological explanation for that surprising finding.
“We were expecting ibuprofen to reduce risk, and the same for aspirin,” says University of Southern California researcher Sarah Marshall.
Alfred Neugut, a Columbia University scientist, says Marshall’s ibuprofen finding is “totally at odds with every other paper” on the subject. Neugut 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.
In a statement Tuesday, American Cancer Society scientist Michael Thun suggested that Marshall’s findings of a higher breast-cancer risk in aspirin or ibuprofen users might be because of chance. “However, it underscores concern about the potential toxicities from long-term regular use of these drugs,” said Thun, co-author of a study 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. When regular aspirin and ibuprofen use more than once a week 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:
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.
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 write, the difference was so small it might have been a result of chance.
No one should stop or start taking a pain reliever because of her study’s findings, Marshall cautions. However, she says, “I’m fairly convinced from our studies that aspirin and ibuprofen are not reducing breast cancer.”