Relationship between aspirin use after diagnosis of colorectal cancer and patient survival: a meta-analysis of observational studies

BACKGROUND: Epidemiological evidence suggests that use of aspirin after the diagnosis of colorectal cancer can lengthen survival. However, the supporting data vary between studies, and this hypothesis remains controversial. We conducted a meta-analysis to provide a quantitative assessment of the association between use of aspirin after diagnosis of colorectal cancer and patient survival. METHODS: We searched the Medline and Embase databases up to April 2014 to identify studies related to aspirin use after diagnosis and all-cause mortality or colorectal cancer-specific mortality. Summary effect estimates with 95% confidence intervals (CIs) were derived using a fixed or random effects model, depending on the heterogeneity between the included studies. RESULTS: Seven epidemiologic studies that consisted of six cohort studies and one nested case–control study were included in this meta-analysis. The hazard ratio (HR) of the association between aspirin use after colorectal cancer diagnosis and overall mortality, which was reported in five studies, was 0.74 (95% CI, 0.62–0.89) using a random model (heterogeneity test P=0.003, I(2)=75.3%), and for colorectal cancer-specific mortality (four studies), it was 0.75 (95% CI, 0.51–1.10) using a random model (heterogeneity test P=0.001, I(2)=84.1%). In addition, we analysed postdiagnosis aspirin use according to whether aspirin was also used before diagnosis. The HR for the overall mortality of patients who did not use aspirin before diagnosis, which was reported in four studies, was 0.84 (95% CI, 0.70–1.00), and for colorectal cancer-specific mortality (three studies), it was 0.79 (95% CI, 0.61–1.02). For those who did use aspirin before diagnosis, the HR for overall mortality (four studies) was 0.88 (95% CI, 0.83–0.93), and for colorectal cancer-specific mortality (three studies), it was 0.80 (95% CI, 0.59–1.09). Subgroup analysis showed that use of aspirin after diagnosis was associated with longer overall survival among patients with the variant PIK3CA gene but not for those with wild-type PIK3CA. CONCLUSIONS: Based on current evidence, the use of aspirin after diagnosis does not reduce colorectal cancer-specific mortality, but it does reduce all-cause mortality for colorectal cancer patients.