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Am Fam Physician. 2021;104(3):online

Clinical Question

Does aspirin increase the risk of cancer in older adults?

Bottom Line

In this large trial, older adults who received aspirin had higher rates of metastatic cancer, stage 4 cancer, and cancer mortality than those who received placebo. (Level of Evidence = 1b)


The Aspirin in Reducing Events in the Elderly trial recruited 19,114 older adults living in Australia and the United States who were 70 years or older (or 65 years or older among U.S. African-American and Hispanic adults) and who were free of known cardiovascular disease, dementia, and physical disability. The researchers randomized the participants (allocation was concealed) to receive a daily dosage of enteric-coated aspirin (100 mg; n = 9,525) or placebo (n = 9,589). The study was terminated after just three years because of an unexpected increase in all-cause mortality in the aspirin-treated group. The authors provided a detailed analysis of the cancer-related outcomes. The researchers reviewed clinical records, including histopathology reports, from treating clinicians and health care institutions when a new or recurrent cancer was reported during the trial follow-up, or after a participant had died. At baseline, the distribution of prior cancer (19%) and known cancer risk factors between the two groups was comparable. The rate of incidental cancer was similar for aspirin- and placebo-treated participants (23.9 vs. 23.0 per 1,000 person-years). Cancer mortality was higher among those treated with aspirin (6.4 vs. 4.8 per 1,000 person-years; number needed to harm [NNH] = 629). The higher mortality is partially explained by higher rates of meta-static cancer (6.1 vs. 5.1 per 1,000 person-years; NNH = 1,006). There was no difference in the rate of hematologic or lymphatic malignancies (2.2 per 1,000 person-years for both groups). The rate of stage 4 cancer was higher in those treated with aspirin (6.5 vs. 5.3 per 1,000-person years; NNH = 839).

Study design: Randomized controlled trial (double-blinded)

Funding source: Government

Allocation: Concealed

Setting: Population-based

Reference: McNeil JJ, Gibbs P, Orchard SG, et al.; ASPREE Investigator Group. Effect of aspirin on cancer incidence and mortality in older adults. J Natl Cancer Inst. 2021;113(3):258–265.

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