Post-menopausal women who have Type 2 diabetes appear to have a 27% greater risk of developing breast cancer, experts say.
An international team, writing in the British Journal of Cancer, examined 40 separate studies looking at the potential link between breast cancer and diabetes.
Being obese or overweight is linked to both conditions.
But cancer experts say there may be a direct connection between the two.
These studies involved more than 56,000 women with breast cancer.
Post-menopausal women with Type 2 diabetes had a 27% increased risk of breast cancer.
But there was no link for pre-menopausal women or those with Type 1 diabetes.
The authors have also suggested that a high body mass index (BMI), which is often associated with diabetes, may be an underlying contributing factor.