Influence of aspirin on prevention of colorectal cancer: an updated systematic review and meta-analysis of randomized controlled trials

Purpose Colorectal cancer is the second most common cause of cancer death worldwide. Aspirin, due to its antineoplastic effects, has been suggested to have chemopreventive effects on colorectal cancer based on recent trials. We conducted this systematic review and meta-analysis to provide an updated evidence about the long-term efficacy of daily aspirin use in the prevention of colorectal cancer. Methods We searched Medline/PubMed, Ovid, Web of Science, and Cochrane Library. We included randomized controlled trials (RCTs) that compared the efficacy of daily aspirin use to placebo in healthy individuals at the time of study entry. The desired outcomes of this review were the incidence of advanced lesions (i.e., adenomas with villous component, adenomas >= 1 cm in diameter, adenomas with high-grade dysplasia, and/or invasive cancer) and colorectal adenomas. Results A total of 15 articles representing 11 RCTs were included. Overall, the results indicated that aspirin significantly reduced the risk of developing colorectal adenomas but not advanced lesions at 3 years (risk ratio (RR) = 0.84, P < 0.05 and risk ratio = 0.82, P = 0.10, respectively). At 5 years, the risk of advanced lesions but not adenomas was reduced by aspirin (RR = 0.68, P < 0.05 and RR = 0.87, P = 0.22, respectively). Aspirin was not found to have an effect on the risk of advanced lesions or adenomas beyond 5 years (hazard ratio (HR) = 0.82, P = 0.07 and HR = 0.99, P = 0.82, respectively). Conclusion Overall, aspirin (particularly high dose) only reduced the risk of advanced lesions up to 5 years.