Effect of low dose and long term use of aspirinin primary prevention of colorectal cancer: Nationwide cohort study, Taiwan 1996-2009

Background: High dose (300 mg+) of aspirin use daily for 5 years is effective in preventing colorectal cancer (CRC) but the effect of lower or less frequent doses of aspirin use in preventing CRC is unknown. Aims: Explore the effect of low dose (<150 mg) of aspirin on preventing CRC. Methods: Hybrid study of cohort with matched comparative group was used and was limited to adults between 18-55 years old. Two longitudinal cohorts of the Taiwan National Health Insurance Research Dataset were used. The low dose group were prescribed <150 mg aspirin daily consecutively for at least 30 days during 1998-2003 and followed until 2010. The nonuse group was matched with the user group by age, gender, three comorbidities (hypertension, DM, hyperlipidemia), index date (the user cases first prescribed aspirin). Records with CRC before aspirin being prescribed were excluded. Results: There were 24032 individuals in the nonuse group, 24032 individuals in the low dose group (3 quarters used aspirin < 3 years, 1 quarter used aspirin > 3 years). There were 149, 102, 19 CRC new cases in the nonuse group, <3 years use group, and >3 years use group, respectively, corresponding to the CRC incidence rate of 52.2, 57.4 and 31.5 per 100,000 person-year, respectively (p=0.0194). The hazard ratio of CRC for the >3 years use group was 0.64 (95% CI, 0.40 and 1.01) multivariately. Conclusions: Marginal benefit of low-dose use of aspirin for >3 years on preventing CRC was seen in Taiwan.