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

OBJECTIVES: 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 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. Additionally, we calculated the number of CRCs 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 ratios [HR]=0.87, 95% confidence intervals [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; Pheterogeneity=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 (Ptrend<0.001). For past use, HRs 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 (Ptrend<0.001). We estimated that aspirin use averted 1073 (95%CI 818-1338) CRCs in the study period.

CONCLUSION: In this nationwide cohort, use of low-dose aspirin was associated with a lower risk of CRC.