Breast Cancer Research and Treatment

, Volume 145, Issue 3, pp 785–790 | Cite as

Metformin may reduce breast cancer risk in Taiwanese women with type 2 diabetes



Whether metformin therapy affects breast cancer risk in Asian patients with type 2 diabetes mellitus (T2DM) has not been investigated. The reimbursement databases of Taiwanese female patients with a new diagnosis of T2DM between 1998 and 2002 (n = 476,282) were retrieved from the National Health Insurance for follow-up of breast cancer until the end of 2009. Metformin was treated as a time-dependent variable; and of these patients, 285,087 were never-users and 191,195 were ever-users. A time-dependent approach was used to calculate breast cancer incidence and estimate hazard ratios by Cox regression for ever-users, never-users, and subgroups of metformin exposure (tertiles of cumulative duration and cumulative dose). During follow-up, 2,412 (1.26 %) metformin ever-users and 9,322 (2.10 %) never-users developed breast cancer, representing an incidence of 201.08 and 535.88 per 100,000 person-years, respectively. The overall multivariable-adjusted hazard ratio (95 % confidence intervals) for ever- versus never-users was 0.630 (0.597–0.665). The multivariable-adjusted hazard ratios for the first, second, and third tertiles of cumulative duration of metformin therapy were 1.122 (1.043–1.207), 0.754 (0.692–0.820), and 0.280 (0.253–0.310), respectively, (P-trend <0.0001); and 1.099 (1.021–1.182), 0.664 (0.611–0.723), and 0.311 (0.281–0.344), respectively, (P-trend <0.0001), for cumulative dose of metformin. Metformin use is associated with a decreased risk of breast cancer.


Breast cancer Diabetes Epidemiology Metformin Taiwan 



The study was supported by the National Science Council (NSC102-2314-B-002-067) of Taiwan.

Conflict of interest



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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  1. 1.Department of Internal MedicineNational Taiwan University College of MedicineTaipeiTaiwan
  2. 2.Division of Endocrinology and Metabolism, Department of Internal MedicineNational Taiwan University HospitalTaipeiTaiwan
  3. 3.Division of Environmental Health and Occupational MedicineNational Health Research InstitutesTaipeiTaiwan

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