Use of aspirin post-diagnosis in a cohort of patients with colorectal cancer and its association with all-cause and colorectal cancer specific mortality.

OBJECTIVE: Aspirin is associated with a reduced risk of developing colorectal cancer. This study examined whether patients with colorectal cancer prescribed aspirin had improved survival.
DESIGN: An observational population cohort study was undertaken using data linkage of cancer registry, dispensed prescriptions and death certificate records in Tayside, Scotland. All community prescribed aspirin pre- and post-diagnosis was extracted and periods of aspirin use post-diagnosis for each individual were analysed using Cox proportional hazard models. Main outcome measures were all-cause and colorectal mortality from death certificates.
RESULTS: Two thousand nine hundred ninety patients were identified with colorectal cancer between 1st January 1997 and 30th December 2006 and followed up until 28th February 2010. Median age at diagnosis was 73 (interquartile range [IQR] 65-80) with 52% male. One thousand nine hundred ninety-eight (67%) deaths were recorded with 1021 (34%) attributed to colorectal cancer. One thousand three hundred forty (45%) patients used aspirin at some stage of the study period. Aspirin use post-diagnosis was associated with lower risk of all cause mortality (hazard ratio [HR]=0.67, 95% confidence interval [CI]=0.57-0.79, p<0.001) and colorectal cancer specific mortality after allowing for age, Dukes' stage, gender, socio-economic status and aspirin use pre-diagnosis. Increasing age and stage at diagnosis were associated with increased risk, with more affluent patients at reduced risk.
CONCLUSIONS: Our study suggests that aspirin use post-diagnosis of colorectal cancer may reduce both all cause and colorectal cancer specific mortality. However further work is required to ensure this is a causal relationship and to identify whether it is best used in specific groups of patients.