Epidemiology

Breast Cancer Research and Treatment

, 98:349

First online:

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

  • Lorraine L. LipscombeAffiliated withInstitute for Clinical Evaluative SciencesDepartment of Medicine, University of TorontoSunnybrook and Women’s College Health Sciences CenterInstitute for Clinical Evaluative Sciences Email author 
  • , Pamela J. GoodwinAffiliated withDepartment of Medicine, University of TorontoDepartment of Health Policy, Management and Evaluation, University of TorontoMount Sinai HospitalSamuel Lunenfeld Research Institute
  • , Bernard ZinmanAffiliated withDepartment of Medicine, University of TorontoMount Sinai HospitalSamuel Lunenfeld Research Institute
  • , John R. McLaughlinAffiliated withDepartment of Health Policy, Management and Evaluation, University of TorontoSamuel Lunenfeld Research Institute
  • , Janet E. HuxAffiliated withInstitute for Clinical Evaluative SciencesDepartment of Medicine, University of TorontoDepartment of Health Policy, Management and Evaluation, University of TorontoSunnybrook and Women’s College Health Sciences Center

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Summary

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.

Keywords

breast cancer cohort study diabetes epidemiology insulin resistance risk