Aspirin is thought to have a potential protective role in several types of cancers, including colorectal, esophageal, gastric, pancreatic, and prostate cancer, but what about in breast cancer (BC)? Results of studies evaluating the impact of aspirin on BC have been mixed, ranging from some showing a modest benefit to others showing no benefit.
To help resolve this matter, researchers conducted a meta-analysis to examine the association between aspirin use and BC risk. Researchers conducted an extensive literature review encompassing PubMed, Embase, Web of Science, Cochrane Library, Scopus, and Google Scholar from January 11, 1939 through October 19, 2019. Additional articles for review were obtained from the reference lists of previous systematic reviews. To be included in the meta-analysis, studies had to evaluate the association between aspirin use and BC risk; have either a randomized, controlled, case-control, or cohort study design; and had to provide either the odds ratio or relative risk (as well as confidence intervals) or include the raw data so that these could be calculated.
Thirty-eight studies met the inclusion criteria, including 22 cohort studies and 16 case-controlled studies. In total, these studies represented 1,926,742 study participants and 97,099 incident BCs. Pathology reports, medical records, and data from cancer registries were screened in 36 studies. Aspirin use was assessed via interview, self-questionnaire, or use of an automated database.
Overall, investigators reported a 9% relative decrease in the risk of BC among aspirin users (relative risk [RR] = 0.91; CI, 0.87-0.95). When study design was considered, a 17% reduction in risk was seen for case-controlled studies compared with cohort studies (RR = 0.96; CI, 0.91-1.02 for cohort studies and RR = 0.83; CI, 0.78-0.89 for case-controlled studies). Studies that utilized an interview (RR = 0.81; CI, 0.73-0.89) to gather data about aspirin use produced more favorable results than those in which a self-administered questionnaire (RR = 0.93; CI, 0.87-1.00) or automated database (RR = 0.96; CI, 0.90-1.02) were utilized. Decreases in BC risk with aspirin use were seen in women with hormone receptor–positive tumors (RR = 0.91; CI, 0.88-0.94) but not in hormone receptor–negative tumors (RR = 1.06; CI, 0.98-1.15).
Aspirin appeared to confer no benefit in premenopausal women (RR = 0.88; CI, 0.72-1.08) but significantly reduced risk in postmenopausal women (RR = 0.89; CI, 0.83-0.96). Women with in situ tumors (RR = 0.79; CI, 0.71-0.88) as opposed to invasive tumors (RR = 1.00; CI, 0.94-1.06) also derived more benefit from aspirin therapy. Longer duration of use (i.e., >10 years, RR = 0.94; CI, 0.89-0.99 versus <10 years; RR = 0.97; CI, 0.94-1.00) and any frequency of use (i.e., >4 times per week , RR = 0.88; CI, 0.82-0.96 or <4 times per week, RR = 0.95; CI, 0.91-0.99), were both statistically significantly associated with reduced risk of BC among aspirin users, although this was less striking with less frequent use.
While the researchers noticed significant heterogeneity among the studies included in this meta-analysis, they did not observe much bias. Proposed mechanisms for aspirin’s possible beneficial effects in BC include inhibition of tumor growth by modulating cellular proliferation and apoptosis; suppression of endogenous production of cyclooxygenase-2 (COX-2) enzyme activity as COX-2 may be overexpressed in BC; decreases in aromatase activity via suppression of COX expression and prostaglandin synthesis; and suppression of tumor-induced angiogenesis. COX-2 enzyme activity has been inversely correlated with estrogen receptor–positive expression.
As the most accessible healthcare professionals, pharmacists are often asked questions about the use of OTC products. They should be knowledgeable about these latest findings regarding aspirin’s potential role in BC so that they can better counsel their patients and help serve as an information bridge to their primary care provider or medical specialist.
The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.
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