Diabetes mellitus and breast cancer: a retrospective population-based cohort study

Breast Cancer Res Treat. 2006 Aug;98(3):349-56. doi: 10.1007/s10549-006-9172-5. Epub 2006 Mar 16.

Abstract

Purpose: 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.

Methods: 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).

Results: 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. 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).

Conclusion: 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.

MeSH terms

  • Age Factors
  • Aged
  • Breast Neoplasms / complications*
  • Breast Neoplasms / diagnosis
  • Breast Neoplasms / epidemiology
  • Breast Neoplasms / metabolism
  • Cohort Studies
  • Diabetes Complications / diagnosis*
  • Diabetes Complications / epidemiology
  • Female
  • Follow-Up Studies
  • Humans
  • Incidence
  • Middle Aged
  • Proportional Hazards Models
  • Time Factors
  • Treatment Outcome