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Impact of aspirin as secondary prevention in an unselected cohort of 25,644 patients with colorectal cancer: A population-based study.
Background: Regular use of aspirin (acetylsalicylic acid) has been associated with reduced incidence and mortality of colorectal cancer (CRC). However, the use of aspirin as primary prevention in the general population is still being debated due to the risk of serious hemorrhagic side effects. In contrast, the use of aspirin as secondary prevention in patients with CRC may be more justified from a risk-benefit prospective, and also as we have observed that aspirin reverses tumor immune evasion mechanisms in established colorectal cancer. This study was conducted to examine the association between aspirin use after diagnosis of CRC with CRC-specific survival (CSS) and overall survival (OS) in the largest cohort ever examined. Methods: An observational population-based retrospective cohort study was undertaken by linking patients diagnosed with CRC from 2004 through 2011 (Cancer Registry of Norway) with the use of aspirin in the same patients (The Norwegian Prescription Database). The registries used cover more than 99% of the Norwegian population, and include all cases in an unselected manner. Exposure was defined as having received prescription for more than 6 months of aspirin after diagnosis of CRC. Multivariate Cox proportional hazard and competing risk analyses were used to model survival. The main outcome measures of the study were CSS and OS. Results: In total, 25,644 patients were diagnosed with CRC in the study period and 6,109 of them were defined as exposed to aspirin after the diagnosis of CRC. The median follow-up was 2.2 years. Among aspirin exposed cases (n = 6,109), a total of 2,088 (34.2%) deaths were recorded of which 1,172 (19.2%) were CRC-specific. Among non-exposed aspirin cases (n = 19,535), a total of 7,595 (38.9%) deaths were recorded of which 6,356 (33.5%) were CRC-specific. In multivariate analysis, aspirin exposure after the diagnosis of CRC was independently associated with improved CSS (hazard ratio [HR], 0.53; 95% confidence interval [CI], 0.50-0.57; p < 0.001) and OS (HR, 0.71; 95% CI, 0.68-0.75; p < 0.001). Conclusions: Exposure to aspirin after the diagnosis of CRC is independently associated with improved CSS and OS.