Women with type 2 diabetes may have increased risk of breast cancer

Women with type 2 diabetes may have an increased risk of breast cancer.

“Evidence suggests that women with type 2 diabetes may be at increased risk of breast cancer, possibly due to chronic exposure to insulin resistance and/or hyperinsulinemia. The purpose of this study was to compare the incidence of breast cancer in postmenopausal women with and without diabetes,” researchers in Canada report.

L.L. Lipscombe and colleagues of the Institute for Clinical Evaluative Sciences explained, “Using population-based validated health databases from Ontario, Canada, this retrospective cohort study compared breast cancer incidence between women, aged 55-79 years, with newly diagnosed diabetes (n=73,796) to women without diabetes (n=391,714). Women with diabetes were slightly older, were more likely to reside in a lower income neighborhood, had greater comorbidity, and had more annual physician visits than women without diabetes.”

“After 2.2 million person-years of follow-up from 1994 to 2002, breast cancer incidence was 2.97/1000 person-years in the diabetes group and 2.75/1000 person-years in the non-diabetes group,” they determined. “After adjustment for age and income, there was a significant increase in breast cancer among women with diabetes (hazard ratio, HR, 1.08, 95% confidence interval, CI, 1.01-1.16, p=0.021).”

The authors concluded, “This study found a small but significant increase in incident breast cancer in a predominantly postmenopausal population of women with diabetes, when compared to women without diabetes. These results support the possibility that insulin resistance or some other aspect of type 2 diabetes may promote breast cancer, and may further direct treatment and prevention strategies.”

Lipscombe and colleagues published their study in Breast Cancer Research and Treatment (Diabetes mellitus and breast cancer: a retrospective population-based cohort study. Breast Cancer Res Treat, 2006;98(3):349-356).

For additional information, contact L.L. Lipscombe, Institute for Clinical Evaluative Sciences, 2075 Bayview Avenue, M4N 3M5, Toronto, Ontario, Canada; Email: .

Publisher contact information for the journal Breast Cancer Research and Treatment is: Springer, 233 Spring Street, New York, NY 10013, USA.