Regular use of aspirin has been linked with a small but significant reduction in the risk for overall cancer, with as much as a 15% reduction in the risk for gastrointestinal tract cancers and a 19% reduction in the risk for colorectal cancers, according to an analysis of data from two large studies published recently in JAMA Oncology.
“The benefit of aspirin for gastrointestinal tract cancers appeared evident with the use of at least 0.5 to 1.5 standard aspirin tablets per week; the minimum duration of regular use associated with a lower risk was 6 years,” wrote study author Yin Cao, MPH, ScD, of the clinical and translational epidemiology unit at Massachusetts General Hospital and Harvard Medical School in Boston, and colleagues.
In 2015, the US Preventive Services Task Force passed a recommendation calling for the use of routine low-dose aspirin among certain subgroups of patients for the prevention of colorectal cancer. However, the task force also recommended continued research looking at the effects of long-term use of aspirin and any effect of aspirin when combined with screening, such as lower endoscopy.
To examine these topics, Cao and colleagues used data from two large prospective studies that included more than 135,000 people: the Nurses’ Health Study and the Health Professionals Follow-Up Study. Both studies reported on aspirin use biennially.
Between the two studies, 20,414 cancers in women and 7,571 cancers in men were recorded. Aspirin data showed that regular aspirin use resulted in a small decrease in the risk for overall cancer (relative risk [RR], 0.97 [95% CI, 0.94–0.99]). This small decrease was driven largely from a 15% decrease in the incidence of gastrointestinal cancers (RR, 0.85 [95% CI, 0.80–0.91]), specifically colorectal cancers (RR, 0.81 [95% CI, 0.75–0.88]).
No association between aspirin use and breast, advanced prostate, or lung cancers was seen.
The benefit of aspirin on colorectal cancer incidence appeared to be dose-dependent (P < .001 for trend). Compared with those patients with no regular aspirin use, use of 0.5 to 1.5 aspirin tablets per week was associated with an RR of 0.86 (95% CI, 0.76–0.97) for colorectal cancer; 2 to 5 tablets, RR of 0.84 (95% CI, 0.75–0.93); for 6 to 14 tablets, RR of 0.76 (95% CI, 0.68–0.86); and 15 or more tablets per week, an RR of 0.61 (95% CI, 0.45–0.81).
“During the first 5 years of use, we did not observe any significant reduction in the risk for cancer compared with nonregular users. Beyond 5 years, we observed a progressively greater reduction in the risk for gastrointestinal tract cancers and colorectal cancers,” the researchers wrote.
They estimated that in people aged 50 or older, regular aspirin use could prevent 33 colorectal cancers per 100,000 person-years among patients who did not undergo screening with lower endoscopy and 18 colorectal cancers per 100,000 person-years among those who did undergo screening.
“Although the relative reduction in overall cancer risk may appear modest, extrapolation of our population-attributable risk estimates to US cancer incidence rates in 2015 indicates that regular aspirin use could prevent more than 29,800 gastrointestinal tract tumors per year, which account for 25% of cancer-related deaths,” the researchers wrote. “Aspirin may be a potential low-cost alternative to endoscopic colorectal cancer screening in resource-limited settings or a complement in settings in which such programs are already implemented, including the general US population, in whom screening adherence remains suboptimal.”