Breast Cancer and Subsequent Risk of Type 2 Diabetes Mellitus: A systematic review and MetaAnalysis

ABSTRACT

Introduction Due to improvements in breast cancer (BC) diagnostics and treatment, the population of BC survivors is growing. BC treatments may have adverse effects that lead to an increased risk of developing type 2 diabetes mellitus (T2D). It is therefore important to investigate the risk of T2D in patients with BC in general and according to type of adjuvant BC treatment. Objectives To conduct a systematic review and meta-analysis investigating the association between early BC and the risk of subsequent T2D diagnosis. A secondary aim was to examine this association according to type of adjuvant BC treatment-chemotherapy and endocrine therapy (ET). Methods We searched PubMed and Embase using variations of the search terms breast cancer (population), ET, tamoxifen, aromatase inhibitors (AIs) and chemotherapy (exposures), and diabetes mellitus (outcome). Two authors screened papers for eligibility by title and using Covidence and reviewed full texts of eligible papers. Guided by the Meta-analysis of Observational Studies in Epidemiology (MOOSE) checklist, study data were extracted. Using random-effects models, we calculated relative risks (RRs) and associated 95% confidence intervals (CIs) for the association between BC, adjuvant BC treatment (ET overall, tamoxifen, and AIs), and subsequent T2D. We used funnel plots to assess publication bias in the analyses. Results Among 16 eligible studies, 11 reported on T2D risk after BC, chemotherapy, or ET;five studies investigated more than one association. Compared with patients without BC, those with BC had elevated risk of T2D overall (RR=1.27, 95%CI=1.15-1.41), particularly those who received any ET (RR=1.23, 95% CI=1.16 1.32). Among BC patients only, risk of T2D was higher for those who received tamoxifen compared with those who did not receive tamoxifen (RR=1.19, 95% CI=1.13-1.25). Due to few studies, analyses investigating T2D risk after treatment with AIs and chemotherapy were inconclusive. Conclusion Our findings support an association between BC and subsequently elevated risk of T2D, particularly after tamoxifen use. Further research is needed to determine the impact of ET overall, AIs and chemotherapy on the incidence of T2D in patients with early BC.