INS and breast cancer: Fasting insulin (OR = 1.71 per SD increase, P = 5.09 × 10–4), two-hour glucose (OR = 1.80 per SD increase, P = 4.02×10–4), BMI (OR = 0.70 per five-unit rise, P = 5.05×10–19, and WHR adjusted BMI (OR=0.85, P=9.22×10-6) all had associations with BC risk. Stratified analyses revealed that genetically predicted fasting insulin was more closely associated with the risk of ER-positive cancer. In contrast, associations with two-hour glucose, BMI, and WHR adjusted BMI was consistent regardless of age, menopausal status, ER status, or family history of BC.