Findings from two large prospective cohort studies published in JAMA Oncology indicated that long-term aspirin use was tied to a modest but significantly reduced risk for overall cancer, especially gastrointestinal (GI) tract tumors. 

The United States Preventive Services Task Force (USPSTF) had recommended aspirin to prevent colorectal cancer and cardiovascular disease among many adults. The association between aspirin use and the risk of other cancer types, and the population-wide effect of aspirin use on cancer especially in regards to screening, is not fully clear. 

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Yin Chao, MPH, ScD, from the Harvard T. H. Chan School of Public Health, Boston, MA, and colleagues, aimed to study the potential benefits of aspirin on the prevention of overall and specific cancer types at various doses and durations. The Nurses’ Health Study (1980–2010) and Health Professionals Follow-up Study (1986–2012) followed up with 135,965 healthcare professionals who reported on aspirin use every 2 years. Final follow-up was on June 30, 2012 and January 31, 2010 for the 2 studies, respectively. 

The main outcome measure was relative risks (RRs) for incident cancers and population-attributable risk (PAR). Of the total patients who were followed up (for as long as 32 years), 20,414 cancers among women and 7.571 cancers among men were documented. 

Regular use of aspirin was associated with a lower risk of overall cancer (RR 0.97, 95% CI: 0.94–0.99), mainly due to a lower incidence of GI tract cancers (RR 0.85, 95% CI: 0.80–0.91), particularly colorectal cancers (RR 0.91, 95% CI: 0.75–0.88). Use of at least 0.5–1.5 standard aspirin tablets weekly demonstrated benefit on GI tract cancers. The minimum duration of regular aspirin use tied to a decreased risk was 6 years. In adults >50 years old, regular aspirin could prevent 33 colorectal cancers per 100,000 person years (PAR 17.05) in those who had not had a lower endoscopy, and prevent 18 colorectal cancers per 100,000 person years (PAR 8.5%) among those who had. 

The risk of breast cancer, advanced prostate, or lung cancer was not associated with regular aspirin use. Study authors concluded that regular aspirin use may prevent a significant proportion of colorectal cancers and complement the benefits of screening. 

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