Diabetes and risk of endometrial cancer: a population-based prospective cohort study.

Although there is accumulating evidence that hyperinsulinemia in the context of insulin resistance is associated with carcinogenesis, only one prospective study of endometrial cancer incidence, in relation to diabetes, addressed this issue and showed no significant positive association. No previous study has investigated whether physical activity can modify the association between diabetes and endometrial cancer. We examined the association between diabetes and incidence of endometrial cancer and the potential effect modification by obesity and physical activity in the Swedish Mammography Cohort, a prospective cohort of 36,773 women, including 225 incident endometrial adenocarcinoma cases. After adjustments, the relative risk (RR) for endometrial cancer among women with diabetes comparing with nondiabetic women was 1.94 [95% confidence interval (95% CI), 1.23-3.08]. Among obese diabetics, the RR was 6.39 (95% CI, 3.28-12.06) compared with nonobese nondiabetic women. Among diabetics with low physical activity, the RR for endometrial cancer was 2.80 (95% CI, 1.62-4.85) compared with physically active nondiabetic women. Obese diabetics with low physical activity had a RR of 9.61 (95% CI, 4.66-19.83) compared with normal weight nondiabetic women with high physical activity. Diabetes was associated with a 2-fold increased risk, and combination of diabetes with obesity and low physical activity was associated with a further increased risk for endometrial cancer. Interventions to reduce body weight and increase physical activity may have important implications in terms of prevention of endometrial cancer and future management of diabetic subjects.