HOMA: homeostatic model assessment; BC: breast cancer; RR: relative risk; HOMA-IR: homeostasis model assessment-insulin resistance; SHBG: sex hormone-binding globulin; IR: insulin resistance; T2DM: type 2 diabetes mellitus; SIR: standardized incidence ratio; HRs: hazard ratios; RFS: recurrence-free survival; OS: overall survival; BCSS: breast cancer-specific survival; BMI: body mass index; ER: estrogen receptor; HER2: human epidermal growth factor receptor 2; HR: hazard ratio; MetS: metabolic syndrome; OR: odds ratio; SD: standard deviation; WHR: waist-hip-ratio; DFS: disease-free survival. Here, ESR1 is linked to type 2 diabetes mellitus.