Aspirin (acetyl salicylic acid), a nonsteroidal anti-inflammatory drug (NSAID), has been linked to reduced risk of breast cancer and its recurrence. However, a major 2024 prospective study reported no benefit of aspirin on breast cancer recurrence and survival among women with high-risk breast cancer.

Aspirin is an NSAID with various activities and side effects

Aspirin is used as a pain killer, fever reducer, and anti-inflammatory drug. Aspirin also has blood-thinning properties and is used long term in low doses to prevent heart attacks (although such use may be declining since daily aspirin has been linked to increased risk of heart failure). Regular aspirin use can have potentially serious side effects, including gastrointestinal bleeding, anemia, hemorrhagic stroke, and age-related macular degeneration.

Aspirin may reduce breast cancer-promoting factors

Aspirin reduces inflammation and inhibits COX-2 overexpression (NSAIDs act by blocking the production of prostaglandins, of which COX-2 is one). Aspirin also might act to reduce circulating sex steroid hormone levels that are associated with increased breast cancer risk — aspirin has been reported to inhibit aromatase activity (in which androgens are converted to estrogens in the body). One study of 740 postmenopausal women in the Nurses' Health Study reported that women who used NSAIDs at least 15 days per month had significantly lower levels of estradiol compared with women with no NSAID use. Frequency of aspirin use was found to be inversely associated with concentrations of estradiol, free estradiol, the ratio of estradiol to testosterone, and estrone sulfate.

Aspirin use before diagnosis of breast cancer

Some studies have found no significant link between aspirin use and risk of breast cancer. However, there are also reports that aspirin use is associated with reduced risk, especially of hormone receptor positive (ER+/PR+) breast cancer. One meta-analysis of data from 33 previous studies reported that aspirin use was associated with a 14% reduction in breast cancer risk compared to no use. Another study reported that aspirin was associated with reduced breast cancer risk in BRCA1 and BRCA2 mutation carriers. A large prospective French study reported that while there was no statistically significant association between NSAID use and breast cancer risk among postmenopausal women, those who also used proton pump inhibitors (PPIs) had lower risk.

Aspirin use after diagnosis

The evidence concerning whether aspirin use after diagnosis reduces risk of recurrence is mixed:
  • A major US 2024 prospective randomized placebo-controlled trial found no breast cancer-free survival benefit in survivors with high-risk nonmetastatic breast cancer who took 300 mg aspirin daily.
  • A Danish 2023 study reported that low-dose aspirin use was associated with a reduced risk of recurrence in the five, ten, and 15 years after breast cancer diagnosis. The effect was highest in the early years.
  • A US 2023 study found that regular aspirin use after diagnosis of nonmetastatic breast cancer was associated with improved long-term survival during up to 32 years of follow-up. Unlike the 2023 Danish study, the advantage of aspirin use (regarding breast cancer-specific mortality) was found to be stronger over time.
  • Another 2023 study reported that aspirin use during remission after initial treatment for inflammatory breast cancer (IBC) was associated with significantly improved distant metastasis-free survival and overall survival.
  • A 2022 study found that women who were unable to achieve pathologic complete response after neoadjuvant chemotherapy had improved outcomes with aspirin use started during the remission period compared to non-aspirin users.
  • Another 2022 study found that regular aspirin use after diagnosis was linked to lower risk of breast cancer-specific mortality, an association that did not differ by breast cancer type.
  • Another study reported that aspirin use was associated with improved survival in women with stage II and stage III triple negative (ER-/PR-/HER2-) breast cancer.
Preliminary evidence suggests that aspirin might enhance the effectiveness of both radiation treatment and tamoxifen. This suggests that aspirin is safe to use as a pain reliever during such treatment, not that it should be used to potentiate it. However, note that aspirin should not be used during chemotherapy since it has the potential to interfere with its treatment effects in some cases.

Aspirin has more favorable profile than other OTC pain killers

For those who can tolerate its side effects, aspirin appears to be a better choice for pain relief and fever reduction than other over-the-counter pain relievers, including acetaminophen (Tylenol), ibuprofen (Advil, Motrin), and naproxen (Aleve). Most studies have reported that acetaminophen, which is not an NSAID, is not associated with risk of breast cancer or its recurrence. Use of ibuprofen has been reported to be associated with increased risk of breast cancer. Naproxen appears to have either a small or no effect in preventing breast cancer. Note that naproxen should not be taken during Adriamycin (doxorubicin) chemotherapy since it has been found to increase Adriamycin-induced heart damage (cardiomyopathy).

Relationship between aspirin use and breast cancer type is unclear

Studies that have examined the association between aspirin use and breast cancer risk by hormone receptor status have produced conflicting results. The reduction in circulating hormones described above suggests that aspirin use could lower the incidence of estrogen receptor positive (ER+) tumors preferentially. However, one large prospective study that examined this question did not find a significant variation by ER status and another reported an insignificant reduction in ER+ risk combined with an increase in the risk of ER- breast cancer.

Food sources of salicylic acid

Aspirin is metabolized into salicylic acid in the body. A wide variety of spices, fruits and other foods contain salicylic acid, although the concentrations are low for the most part. The average daily intake of salicylic acid from foods has been estimated at 0 to 5 mg. Note that drying concentrates the salicylic acid levels of a food. Also note that those with salicylic acid sensitivity should limit or avoid these foods. Below are foods that are good sources of salicylic acid, in addition to having been linked to reduced breast cancer risk:
One study which reported that breast cancer risk was elevated among women who ate meat, especially flame broiled meat, also found that aspirin use reduced the meat consumption-related increase in breast cancer risk.
The bark of the white willow tree (Salix alba) contains salicin, which is similar to aspirin. However, white willow bark supplements can be a source of cadmium exposure due to uptake of cadmium in the soil by the tree.

Bottom line

Attempting to use aspirin as a treatment for breast cancer appears ill-advised, partially because its effectiveness is not established and also because of aspirin's potentially serious side effects. However, it appears to be a good over-the-counter choice to relieve pain and inflammation.

Sources of information in this webpage

The information above, which is updated continually as new research becomes available, has been developed based solely on the results of academic studies. Clicking on any of the underlined terms will take you to its tag or webpage, which contain more extensive information.
Below are links to 20 recent studies concerning this topic. For a more complete list of studies, please click on aspirin.