Context Risk of cancer is a major concern in the development of drugs for the treatment of obesity and diabetes. In randomized controlled trials (RCTs) of the liraglutide development program, a glucagon-like peptide-1 receptor agonist (GLP-1RA), subjects treated with the active drug had a higher absolute number of breast cancer events. Objective To assess whether patients treated with GLP-1RAs had a higher risk of breast neoplasms. Data sources We searched MEDLINE, Embase, Web of Science, and CENTRAL from inception to February 8, 2020. Study Selection Reviewers assessed abstracts and full-text articles for RCTs of GLP-1RAs in adults with excessive weight and/or diabetes and a minimum follow-up of 24 weeks. Data extraction Researchers extracted study-level data and assessed within-study risk of bias with the RoB 2.0 tool and quality of evidence with GRADE. Data synthesis We included 52 trials, of which 50 reported breast cancer events and 11 reported benign breast neoplasms. Overall methodological quality was high. Among 48267 subjects treated with GLP-1RAs, 130 developed breast cancer compared to 107 of 40755 controls (relative risk [RR], 0.98; 95% confidence interval [CI], 0.76 to 1.26). Subset analyses according to follow-up, participant/investigator blinding, and type of GLP-1RA did not reveal any differences. The risk of benign breast neoplasms also did not differ between groups (RR, 0.99; 95% CI, 0.48 to 2.01). Trial sequential analysis provided evidence that the sample size was sufficient to avoid missing alternative results. Conclusions Treatment with GLP-1RAs for obesity and diabetes does not increase the risk of breast neoplasms.

Background: Risk of cancer is a major concern in the development of drugs for the treatment of obesity and diabetes. In randomized controlled trials (RCTs) of the liraglutide development program, a glucagon-like peptide-1 receptor agonist (GLP-1RA), subjects treated with the active drug had a higher absolute number of breast cancer events. Aim: To assess whether patients treated with GLP-1RAs had a higher risk of breast neoplasms. Methods: We searched MEDLINE, Embase, Web of Science, and CENTRAL from inception to February 8, 2020. Three pairs of reviewers examined and retrieved abstractsand full-text articles for RCTs of GLP-1RAs versus non-GLP-1RA controls(active or placebo) in adults with overweight, obesity, prediabetes, or diabetes,with a minimum follow-up period of 24 weeks and which reported at least oneevent of breast cancer or benign breast neoplasm. Divergences were dealt withby consensus. Researchers extracted study-level data and assessed within-study risk of bias with the RoB 2.0 tool and quality of evidence with GRADE. This study follows PRISMA reporting guidelines. Results: We included 52 trials, of which 50 reported breast cancer events and 11 reported benign breast neoplasms. Overall methodological quality was high. Among 48267 subjects treated with GLP-1RAs, 130 developed breast cancer compared to 107 of 40755 controls (relative risk [RR], 0.98; 95% confidence interval [CI], 0.76 to 1.26). Subset analyses according to follow-up, participant/investigator blinding, and type of GLP-1RA did not reveal any differences. The risk of benign breast neoplasms also did not differ between groups (RR, 0.99; 95% CI, 0.48 to 2.01). Trial sequential analysis provided evidence that the sample size was sufficient to avoid missing alternative results. Conclusion: Treatment with GLP-1RAs for obesity and diabetes does not increase the risk of breast neoplasms. Register: This systematic review was preregistered in PROSPERO (CRD42019132704).