Diabetes Mellitus and Risk of Breast Cancer: A Large-Scale, Prospective, Population-Based Cohort Study

Background: A previous meta-analysis identified a weak association between diabetes and breast cancer (BCa) risk among postmenopausal women. The heterogeneity among studies, however, was substantial, and many of the included studies were susceptible to residual confounding by body mass index (BMI) and other BCa risk factors. The objective of this study was to evaluate associations of diabetes overall, type 1 diabetes (T1D) , and type 2 diabetes (T2D) with BCa risk within the UK Biobank cohort. Methods: We included 250,312 women aged 40-69 years between 20 and 2010, who were free of cancer at enrollment. Multivariable Cox regression models were performed to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for associations of diabetes and its two major types with the time from enrollment to incident BCa. Results: We identified 8182 BCa diagnoses during a median follow-up of 11.1 years. We found no overall association between diabetes and BCa risk (adjusted HR [aHR] = 1.03, 95% CI = 0.93- 1.15) . When further accounting for diabetes subtype, T2D did not demonstrate a significant association with BCa (aHR = 1.01, 95% CI = 0.90- 1.12) . Women with T1D, however, had a higher risk of BCa than women without diabetes (aHR = 1.51, 95% CI = 1.03 - 2.22) . The associations of diabetes, T1D, and T2D with BCa did not vary by age, menopausal status, BMI, or other BCa risk factors. Conclusions: We did not observe associations between diabetes or T2D and BCa among women within the UK Biobank. However, our data suggested that women with T1D may have an increased risk of BCa. Larger studies are warranted to investigate the relationship of T1D with BCa and its subtypes. Disclosure F. Xiong: None. J. Wang: None. J.L. Nierenberg: None. G. Schmajuk: None. R.E. Graff: None.