Impaired glucose metabolism and diabetes and the risk of breast, endometrial, and ovarian cancer.

Background: Epidemiological evidence indicates that individuals with type 2 diabetes are at an increased risk of cancer. Elevated glucose levels, below the diagnostic threshold for diabetes, have also been suggested to be associated with increased cancer risks.
Methods: We investigated possible associations between glucose levels and the risk of breast, endometrial, and ovarian cancer in a cohort of more than 230,000 women, for which information on outcome and potential confounders was obtained by record linkage to population-based registers.
Results: Diabetes was associated with an increased risk of postmenopausal breast cancer (HR = 1.22, 95% CI 1.04-1.43). An indication of a slightly elevated breast cancer risk was also found in postmenopausal women with impaired glucose metabolism (HR = 1.11, 95% CI 0.96-1.28). Diabetes (HR = 1.46, 95% CI 1.09-1.96) and impaired glucose metabolism (HR = 1.41, 95% CI 1.08-1.85) were associated with an increased risk of endometrial cancer. No associations were found between glucose levels and ovarian cancer risk. Following adjustment for BMI, estimates were attenuated for endometrial cancer, while point estimates for breast and ovarian cancer remained essentially unchanged.
Conclusions: Our results indicate that glucose levels below the diagnostic threshold for diabetes modify the risk not only of endometrial cancer but possibly also of postmenopausal breast cancer.