Incidence of colorectal cancer in new users and non-users of low-dose aspirin without existing cardiovascular disease: A cohort study using The Health Improvement Network

Abstract

BackgroundEvidence regarding the chemo-protective effects of aspirin has influenced expert opinion in favour of low-dose aspirin use in certain patient populations without cardiovascular disease (CVD). The effects of aspirin in reducing the incidence of colorectal cancer (CRC) may be a large contributor to this favourable risk–benefit profile of low-dose aspirin in primary CVD prevention. MethodsUsing The Health Improvement Network, we estimated the incidence of CRC in individuals free of CVD and either prescribed or not prescribed prophylactic low-dose aspirin. Two cohorts – new-users of low-dose aspirin (N=109,426) and a comparator cohort of non-users (N=154,056) at start of follow-up – were followed (maximum 13years) to identify incident CRC cases. Individuals with a record of CVD, cancer or low-dose aspirin prescription before start of follow-up were excluded. Results2330 incident cases of CRC occurred; 885 in the aspirin cohort and 1445 in the comparator cohort, after mean follow-ups of 5.43years and 5.17years, respectively. Incidence rates of CRC per 10,000 person-years (95% confidence interval) were 14.90 (13.95–15.92) in the aspirin cohort and 18.15 (17.24–19.12) in the comparator cohort; incidence rate ratio 0.82 (0.76–0.89) adjusted for age, sex and primary care practitioner (PCP) visits in the previous year. Lower incidence rates were seen in the aspirin cohort for all strata evaluated (gender, age group and number of PCP visits in the previous year) except those aged ≥80years. ConclusionAmong most individuals without established CVD, initiation of low-dose aspirin is associated with a reduced incidence of CRC.