Low-dose aspirin and prevention of colorectal cancer: evidence from a nationwide registry-based cohort in Norway

INTRODUCTION: To examine the association between low-dose aspirin use and risk of colorectal cancer (CRC). METHODS: In this nationwide cohort study, we identified individuals aged 50 years or older residing for 6 months or more in Norway in 2004–2018 and obtained data from national registers on drug prescriptions, cancer occurrence, and sociodemographic factors. Multivariable Cox regression models were used to estimate the association between low-dose aspirin use and CRC risk. In addition, we calculated the number of CRC potentially averted by low-dose aspirin use. RESULTS: We included 2,186,390 individuals. During the median follow-up of 10.9 years, 579,196 (26.5%) used low-dose aspirin, and 38,577 (1.8%) were diagnosed with CRC. Current use of aspirin vs never use was associated with lower CRC risk (hazard ratio [HR] 0.87, 95% confidence interval [CI] 0.84–0.90). The association was more pronounced for metastatic CRC (HR 0.79; 95% CI 0.74–0.84) than regionally advanced (HR 0.89; 95% CI 0.85–0.92) and localized CRC (HR 0.93; 95% CI 0.87–1.00; P heterogeneity = 0.001). A significant trend was found between duration of current use and CRC risk: HR 0.91 (95% CI 0.86–0.95) for <3 years, HR 0.85 (0.80–0.91) for ≥3 and <5 years, and HR 0.84 (0.80–0.88) for ≥5 years of use vs never use ( P trend < 0.001). For past use, HR were 0.89 (95% CI 0.84–0.94) for <3 years, 0.90 (0.83–0.99) for ≥3 and <5 years, and 0.98 (0.91–1.06) for ≥5 years since last use vs never use ( P -trend < 0.001). We estimated that aspirin use averted 1,073 cases of CRC (95% CI 818–1,338) in the study period. DISCUSSION: In this nationwide cohort, use of low-dose aspirin was associated with a lower risk of CRC.