The effect of regular use of either over-the-counter (OTC) non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen (e.g., Advil and Motrin), or prescription NSAIDs on the risk of developing breast cancer is controversial. Some studies performed previously suggested that regular use of aspirin or ibuprofen may help protect against developing certain types of breast cancer, whereas the findings of a recent study imply that regular use of aspirin or ibuprofen may raise the risk of developing certain types of breast cancer.
Based on past studies, many physicians believed that regular use of NSAIDs could help prevent the development of certain types of breast cancer. In some studies, women who regularly took the non-steroidal anti-inflammatory drugs (NSAIDs), aspirin or ibuprofen (e.g., Advil and Motrin), had a slightly lower risk of developing hormone-receptor-positive breast cancer (i.e., breast tumors that have receptors to estrogen or progesterone on the surface of the cells).[1, 2]
In contrast, regular use of aspirin or ibuprofen was not associated with reducing the risk of developing hormone-receptor-negative breast cancer (i.e, breast tumors that lack receptors to estrogen or progesterone on the surface of the cells).[1, 2]
Several studies demonstrate that another type of pain-reliever, acetominophen (e.g., Tylenol, which is not an NSAID), had no protective effects against the development of either hormone-receptor-positive or hormone-receptor-negative breast cancer.
In a study of past use of medications in women with newly-diagnosed breast cancer:[1, 2]
Daily use of aspirin for at least 6 months was associated with a 28% lower risk of hormone-receptor-positive breast cancer
Once weekly use of aspirin for at least 6 months was associated with a 20% lower risk of hormone-receptor- positive breast cancer
Regular use of ibuprofen (e.g., Advil and Motrin) was less effective than was aspirin in lowering the risk of hormone- receptor-positive breast cancer
Several theories have been offered to explain the protective effect of aspirin and ibuprofen against the development of breast cancer in past studies. Researchers believed that aspirin and ibuprofen may help prevent breast cancer by blocking the COX-2 enzyme, which otherwise could stimulate the growth of cancer cells.
Also, aspirin and ibuprofen can inhibit the synthesis of a hormone-like substance (prostaglandin) that normally would activate the expression of (i.e., turn on) the gene coding for the aromatase enzyme, which is involved in the production of estrogen. [1, 2,5] Therefore, use of aspirin and ibuprofen may lower the level of estrogen in breast tissue and other parts of womens bodies. A decrease in estrogen levels is thought to be responsible for the reduced risk of hormone-receptor- positive breast cancer observed in women who regularly took aspirin or ibuprofen in past studies.[1, 2, 5]
However, not all studies have demonstrated a link between regular use of NSAIDs and reduced risk of breast cancer in general or even specific types of breast cancer. A recent report based on a 6-year analysis of medications taken and the health status of over 114,000 women in the California Teacher's Study suggests that regular use of aspirin or ibuprofen may raise the risk of breast cancer slightly.[3, 4, 6]
To put the statistics in perspective, during the 6 years of the study, nearly 2,400 of the women were diagnosed with breast cancer.  Of the women diagnosed with breast cancer during the study, some did not have a history of taking NSAIDs regularly, whereas others did take NSAIDs regularly prior to their diagnosis. Although the frequency of aspirin or ibuprofen use was examined, the study did not include analysis of the effects of different doses of the medications.
The frequency and type of NSAID medication used appeared to affect the risk of breast cancer. Women who took aspirin or ibuprofen more often than once weekly but less often than once daily had a similar risk of developing breast cancer, when compared to that of women who took aspirin or ibuprofen less often than once weekly.
Regular daily use of aspirin for a period of at least 5 years was associated with an 81% higher risk of developing a less common type of breast cancer, known as hormone receptor-negative breast cancer (i.e., breast tumors that lack receptors for estrogen and progesterone on the surface of the cells). In the group of women who used aspirin daily for at least 5 years, 7 additional cases of hormone receptor-negative breast cancer were diagnosed, compared to the occurrence in the group of women who did not use either aspirin or ibuprofen regularly.
Regular daily use of ibuprofen for a period of at least 5 years was associated with a 51% higher risk of breast cancer in general, and a 92% higher risk of occurrence of advanced stages of breast cancer (i.e., breast cancer that has spread beyond the breast to other parts of the body). In the group of women who used ibuprofen daily for at least 5 years, 24 additional cases of hormone receptor-negative breast cancer were diagnosed, compared to the occurrence in the group of women who did not use either ibuprofen or aspirin regularly.
Despite the new findings from the California Teachers Study, scientists and physicians do not know whether regular, long-term use of aspirin or ibuprofen actually can cause certain types of breast cancer. Therefore, more clinical studies need to be performed to determine whether long-term use of certain doses of different NSAIDs by women increases, does not affect, or lowers the risk of various types of breast cancer.
Remember that, as is the case with all medications, aspirin and ibuprofen have side effects. For example, long-term use of aspirin, ibuprofen, or other non-steroidal inflammatory drugs (NSAIDs) can result in: [1, 2]
Irritation, bleeding, and ulcers in the stomach and the rest of the digestive system
Bleeding in the urinary tract
Bleeding in the brain that can cause hemorrhagic stroke
Due to the possibility of serious side effects, people who should not take regular aspirin, ibuprofen, or other non-steroidal inflammatory drugs regularly include those with a medical history of:
Although some women take aspirin daily to prevent cardiovascular events, no formal recommendations or standard doses of aspirin or ibuprofen to help prevent breast cancer in women at either "average" or high risk have ever been established.
Before considering whether to include regular use of aspirin or ibuprofen to help you prevent or treat any diseases, discuss your medical history with your doctor to determine whether use of these medications are appropriate for you. Do not discontinue use of aspirin or ibuprofen that your doctor has recommended previously, without consulting your doctor first.
Whether or not you and your doctor decide that taking aspirin or ibuprofen regularly is right for you, be sure to adopt the many healthy lifestyle choices (e.g., a sensible diet that lowers the likelihood of chronic inflammation in your body, regular exercise, avoidance of smoking, etc.) that have the power to help you maintain breast health, prevent breast cancer, and improve your overall wellness.
1. Preventing breast cancer: Lifestyle choices and other factors you can control. Accessed at www.mayoclinic.com
2. M.B. Terry, M.D. Gammon, F.F. Shang, H. Tawfik, et al. Association of frequency and duration of aspirin use and hormone receptor status with breast cancer risk. Journal of the American Medical Association. 2004; 291(20):2433-2440.
3. S. Boyles. Aspirin doesn't prevent breast cancer. WebMDHealth. 05/31/05. Accessed at www.webmd.com.
4. National Cancer Institute. Study finds breast cancer risk with NSAID use. NCI Cancer Bulletin. 2005; 2(23):2.
5. R.N. DuBois. Aspirin and breast cancer prevention: The estrogen connection. Journal of the American Medical Association. 2004; 291(20):2488-2489.
6. R. Rubin. Can aspirin raise breast cancer risk? New study contradicts other findings on risk. Gannet News Services. 06/01/05.