Metformin and other anti-diabetic medication use and breast cancer incidence in the Nurses' Health Studies

Tengteng Wang; Boyang Chai; Wendy Y Chen; Michelle D Holmes; Jennifer Erdrich; Frank B Hu; Bernard A Rosner; Rulla M Tamimi; Walter C Willett; Jae H Kang; A Heather Eliassen

doi:10.1002/ijc.34917

Metformin and other anti-diabetic medication use and breast cancer incidence in the Nurses' Health Studies

Int J Cancer. 2024 Mar 22. doi: 10.1002/ijc.34917. Online ahead of print.

Authors

Tengteng Wang^{1

2

3}, Boyang Chai³, Wendy Y Chen^{3

4}, Michelle D Holmes^{3

5}, Jennifer Erdrich⁶, Frank B Hu^{3

7}, Bernard A Rosner^{3

8}, Rulla M Tamimi⁹, Walter C Willett⁷, Jae H Kang³, A Heather Eliassen^{3

5

7}

Affiliations

¹ Cancer Epidemiology and Health Outcomes, Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey, USA.
² Division of Medical Oncology, Robert Wood Johnson Medical School, New Brunswick, New Jersey, USA.
³ Channing Division of Network Medicine, Brigham & Women's Hospital, Boston, Massachusetts, USA.
⁴ Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA.
⁵ Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, USA.
⁶ Department of Surgery, The University of Arizona, Tucson, Arizona, USA.
⁷ Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, USA.
⁸ Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, USA.
⁹ Department of Population Health Sciences, Weill Cornell Medicine, New York, New York, USA.

PMID: 38520039
DOI: 10.1002/ijc.34917

Abstract

We aimed to examine the association between the use of metformin and other anti-diabetic medications and breast cancer incidence within two large prospective cohort studies. We followed 185,181 women who participated in the Nurses' Health Study (NHS; 1994-2016) and the NHSII (1995-2017), with baseline corresponding to the date metformin was approved for type 2 diabetes (T2D) treatment in the US Information on T2D diagnosis, anti-diabetes medications, and other covariates was self-reported at baseline and repeatedly assessed by follow-up questionnaires every 2 years. Breast cancer cases were self-reported and confirmed by medical record review. Hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between medication use and breast cancer were estimated using Cox proportional hazards regression models, adjusting for breast cancer risk factors. During 3,324,881 person-years of follow-up, we ascertained 9,192 incident invasive breast cancer cases, of which 451 were among women with T2D. Compared with women without T2D (n = 169,263), neither metformin use (HR = 0.97; 95% CI = 0.81-1.15) nor other anti-diabetic medications use (HR = 1.11; 95% CI = 0.90-1.36) associated with significantly lower breast cancer incidence. Among women with T2D (n = 15,918), compared with metformin never users, metformin ever use was not significantly inversely associated with breast cancer (HR = 0.92; 95% CI = 0.74-1.15). Although we observed that past use of metformin was inversely associated with breast cancer in the T2D population (HR = 0.67; 95% CI = 0.48-0.94), current use (HR = 1.01; 95% CI = 0.80-1.27) and longer duration of metformin use were not associated with breast cancer (each 2-year interval: HR = 1.01; 95% CI = 0.95-1.07). Overall, metformin use was not associated with the risk of developing breast cancer among the overall cohort population or among women with T2D.

Keywords: breast cancer; diabetes mellitus; metformin.

Abstract

Grants and funding