Does low-dose aspirin use for cardiovascular disease prevention reduce colorectal cancer deaths? A comparison of two cohorts in the Florence district, Italy.

Aspirin has been associated with reduced incidence and mortality of colorectal and a few other cancers. The aim of our paper was to study the effect of low-dose aspirin intake on cancer mortality in a population-based cohort study. The study included inhabitants of the Florence district (Italy) at the beginning of 2007. We considered two cohorts: patients who received prescriptions of low-dose aspirin for the whole year and patients who did not have any prescriptions over the same period. We followed the two cohorts until 31 December 2013. By linking with the Tuscany Mortality Registry, we analysed cause-specific mortality. We used a Cox semiparametric model to compare the mortality of the two cohorts. There was an 18% higher probability [hazard ratio (HR)=1.18, 95% confidence interval (CI): 1.12-1.23] for all causes of death among the cohort of aspirin users, almost completely caused by cardiovascular diseases (CVDs) (HR=1.39, 95% CI: 1.29-1.49). Colorectal cancer mortality was reduced by almost 30% (HR=0.71, 95% CI: 0.52-0.97). Death caused by major bleeding was 11% higher (HR=1.11, 95% CI: 0.86-1.44), but not statistically significant. Our results support the hypothesis that the use of low-dose aspirin for CVD prevention reduces colorectal cancer mortality. Given the growing ability to identify subgroups of individuals with an increased risk of developing cancer, further studies are needed to study the effectiveness of different cancer screening strategies tailored to these specific subgroups. Our study suggests the importance of focusing on this issue from the opposite perspective, that is, considering subgroups of individuals at decreased risk, such as the subgroup of individuals who take low-dose aspirin for CVD prevention. Thus, further assessments are needed to possibly identify subgroup-specific screening strategies that would be more effective than those developed for average-risk individuals.