Ibuprofen use is associated with an increased risk of breast cancer, and long-term daily use of aspirin is associated with an increased risk of estrogen receptor/progesterone receptor (ER/PR)-negative breast cancer, according to a new study in the June 1 issue of the Journal of the National Cancer Institute.

Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen, are used to treat common conditions such as pain and fever and chronic conditions such as arthritis and are given prophylactically to reduce the risk of heart attacks and stroke. Interest has also been growing in using NSAIDs to prevent cancer. Studies have found an inverse association between NSAID use and colorectal cancer, but studies of NSAIDs and breast cancer risk have had mixed results.

To investigate the association between NSAID use and breast cancer risk, Sarah F. Marshall, of the University of Southern California in Los Angeles, and colleagues analyzed data on 114,460 women in the California Teachers Study cohort who were ages 22 to 85 and free of cancer at the baseline of the study, 1995 to 1996. During the follow-up period, 1995 to 2001, 2,391 women were diagnosed with breast cancer of known receptor status.

Regular use (i.e., more than once a week) of NSAIDs was not associated with breast cancer risk. However, long-term daily use of aspirin was associated with an increased risk of ER/PR-negative breast cancer, and long-term daily use of ibuprofen was associated with an increased risk of breast cancer and particularly nonlocalized cancer.

"These observations warrant further exploration because of the public health impact such readily available NSAIDs may have on breast cancer," the authors write. "Additional large-scale prospective epidemiologic studies may help clarify the findings by further examining the long-term effects of aspirin and ibuprofen, especially with regard to ER/PR-negative and nonlocalized breast cancer. A more detailed understanding of the tissue-specific effects of NSAIDs, particularly in the context of the complex biological mechanisms involved in the development of different cancers, is also needed."