A 20-year population-wide cohort study on association of aspirin and risk of gastrointestinal and non-gastrointestinal cancer.
Authors: Tsoi Kelvin KF , Sung Joseph J.Y. 
Published: January 2025

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Background:
Aspirin has been shown to reduce the risk of various gastrointestinal (GI) and non-GI cancers
1,2
. However, little was known about at what age aspirin should be started for maximal chemoprotective better on GI cancer. Furthermore, the randomised controlled trial on aspirin for primary prevention use in healthy elderly (ASPREE) showed no association between aspirin and cancer incidence despite the limitation of short follow-up duration
3
. The current study aims to investigate the 20-year risk of cancer using aspirin in a territory-wide Hong Kong population cohort.
Methods:
The study included all aspirin users from 2000 to 2019, and non-aspirin users matched by age and sex at a ratio of 1:2. Enrolled subjects with a history of cancer at enrolment, cancer incidence or death within 6 months were excluded. The incidence of individual GI and non-GI cancer was presented as the primary outcome. Baseline characteristics between aspirin and non-aspirin users were adjusted in the survival analysis by inverse probability of treatment weighting (IPTW). The fine-grey model has been used to address bias from competing risk of death. The sub-distribution hazard ratio was presented for the association of aspirin use and risk of GI and non-GI cancers.
Results:
The current study included 538,147 aspirin users and 968,378 non-users with a mean age of 64.8 years. A total number of 36,683 cases of GI cancer (2.4%) and 47,196 cases of non-GI cancers (3.1%) were observed. Aspirin was associated with a lower risk of several common individual GI cancers, including colorectal cancer (SHR 0.78, 95% CI 0.76-0.81), liver cancer (SHR 0.67, 95% CI 0.64-0.70), stomach cancer (SHR 0.79, 95% CI 0.75-0.84) and pancreatic cancer (SHR 0.85, 95% CI 0.79-0.91), but not oesophageal cancer. On the other hand, aspirin was associated with a lower risk of prostate cancer (SHR 0.95, 95% CI 0.91-1.00) and breast cancer (SHR 0.76, 95% CI 0.73-0.79), but not lung cancer and kidney cancer. In overall, aspirin was associated with a 24% lower risk of GI cancers (SHR 0.76, 95% CI 0.74-0.78) and a 3% lower risk of non-GI cancers (SHR 0.97, 95% CI 0.95-0.99).
Conclusions:
Aspirin was associated with a lower risk of most GI cancers, including colorectal cancer, liver cancer, stomach cancer and pancreatic cancer, but not most non-GI cancers. In general, results on the effect of aspirin on GI cancer prevention were consistent with the previously presented 10-year cohort. 1. Bosetti C, Santucci C, Gallus S, Martinetti M, La Vecchia C. Aspirin and the Risk of Colorectal and Other Digestive Tract Cancers: An Updated Meta-analysis through 2019. Ann Oncol. 2020;31(5):558-568. 2. Santucci C, Gallus S, Martinetti M, La Vecchia C, Bosetti C. Aspirin and the risk of nondigestive tract cancers: An updated meta-analysis to 2019. Int J Cancer. 2021;148(6):1372-1382. 3. McNeil JJ, Gibbs P, Orchard SG, et al. Effect of Aspirin on Cancer Incidence and Mortality in Older Adults. J Natl Cancer Inst. 2021;113(3):258-265.