Long-term aspirin use for cancer primary prevention A protocol for updated systematic review and subgroup meta-analysis of randomized clinical trials

Background: Long-term use of aspirin for primary prevention of cancer remains inconclusive, and variation in the effects of aspirin use on cancer outcomes by cancer site, aspirin dose, follow-up duration, or different populations has never been systematically evaluated. Methods: Seven electronic databases (PubMed, EMBASE, ClinicalTrials.gov, etc) will be searched from inception to September 30, 2019. Randomized clinical trials (RCTs) comparing aspirin versus no aspirin in participants without pre-existing cancer and reporting cancer incidence, and/or cancer mortality outcomes will be selected and assessed for inclusion. The Cochrane's Risk of Bias Tool and the Jadad scale will be used to evaluate the risk of bias and the methodologic quality of the RCTs. Data will be screened and extracted by independent investigators. Total cancer incidence will be defined as the primary clinical endpoint, and total cancer mortality, all-cause mortality, and the risk of major bleeding will be the secondary outcomes. Subgroup analyses based on cancer site, aspirin dose, follow-up duration, or different populations will be conducted. Analyses will be performed using Review Manager 5.3, Comprehensive Meta-Analysis 2.0, and Trial Sequential Analysis (TSA) software. Results: This study will systematically evaluate the effects of long-term aspirin use on total cancer incidence, cancer mortality, allcause mortality, and the risk of major bleeding. Subgroup analyses will indicate whether the effects of aspirin on cancer outcomes are associated with cancer site, daily dose of aspirin, follow-up duration, or different subgroup of participants. The results will be submitted and published in a peer-reviewed scientific journal. Conclusions: This systematic review will systematically evaluate the efficacy and safety of long-term use of aspirin for primary prevention of cancer and determine whether there are some potential influencing factors affecting the effects of aspirin on cancer outcomes, thus strengthening the evidence base for the clinical practice and future research of this intervention.