The association between low-dose aspirin use and the incidence of colorectal cancer: A nationwide cohort study

Background Considerable evidence suggests that aspirin has a chemopreventive effect on colorectal cancer (CRC). However, optimal dose and treatment duration have not been defined, and data on the effects of low-dose aspirin are contradictory. Aim To determine if the incidence of CRC in patients with low-dose aspirin use was lower than in those without aspirin use. Method From Taiwan's National Health Insurance research database, aspirin users (n = 1985) were defined as adults (age ≥20 years) with at least 3.5 years of regular low-dose aspirin use (50-150 mg per day) between 1998 and 2002. Non-users (n = 7940) were those who did not use aspirin and were matched 4:1 with the user group by age, gender, date of ambulatory care (index date), and presence of known risk factors for cardiovascular disease (including hypertension, diabetes mellitus and hyperlipidaemia). Follow-up of the two study groups was made until the end of 2010, and incidences and hazard ratios of colorectal cancer were determined. Results During a median follow-up period of 8.9 years, 129 non-users and 14 users developed CRC, corresponding to incidence rates of 180.43 and 79.42 per 100 000 person-years respectively. Duration of aspirin use among users ranged from 3.5 to 12.6 years (mean 8.7 years). The multivariate-adjusted hazard ratio for CRC was 0.5 (95% confidence interval 0.28-0.87) among users as compared with non-users. Conclusions Long-term use of low-dose aspirin appears to be associated with a lower incidence of CRC in patients with high cardiovascular risk. Further randomised clinical trials are necessary to confirm these findings.