Low‐dose aspirin use and colorectal cancer survival in 32,195 patients—A national cohort study

BACKGROUND: Results from previous studies indicate that use of aspirin may improve colorectal cancer (CRC) survival. The aim of this study was to assess whether use of aspirin influences overall survival or CRC‐specific survival in an unselected cohort of patients diagnosed with CRC. METHODS: The study was performed using the Colorectal Cancer Data Base Sweden (CRCBaSe), a mega‐linkage originating from the Swedish Colorectal Cancer Register, with additional linkages to other national health care registers. All patients diagnosed with primary CRC stage I–III treated with curative surgery, aged 18–85 years at diagnosis, from 2007 through 2016 were identified. Information on low‐dose aspirin use was extracted from the Swedish Prescribed Drug Register. Exposure was defined as dispensed prescription for at least 6 months. Aspirin exposure was analyzed at the time of surgery (yes/no) and as a time‐varying exposure during follow‐up. Follow‐up was restricted to a maximum 6 years, to model 5‐year survival. Cox regression models were fitted to estimate hazard ratios (HRs) with 95% confidence intervals (CIs). Adjustments were performed for sex, age, year of diagnosis, Charlson comorbidity index, hypertension, and ASA score as potential confounders. RESULTS: A total of 32,195 patients diagnosed with CRC were included. 6764 (21%) were exposed to aspirin at the time of CRC surgery. The median time of follow‐up was 4.2 years. Aspirin use at the time of surgery was not associated with all‐cause (adjusted HR = 1.03, 95% CI: 0.97–1.08) nor CRC‐specific mortality (adjusted HR = 0.99, 95% CI: 0.91–1.07). Aspirin use during follow‐up was associated with increased all‐cause (adjusted HR = 1.09, 95% CI: 1.04–1.15) but not CRC‐specific mortality (adjusted HR = 0.98, 95% CI: 0.91–1.06). A CRC‐specific effect associated with aspirin was noted from approximately 3 years following surgery. CONCLUSIONS: In this large nation‐wide cohort study there was no convincing association between aspirin use after CRC and OS or CRC‐specific survival.