Acta Diabetologica

, Volume 51, Issue 2, pp 295–303

Metformin may reduce bladder cancer risk in Taiwanese patients with type 2 diabetes

Original Article

DOI: 10.1007/s00592-014-0562-6

Cite this article as:
Tseng, CH. Acta Diabetol (2014) 51: 295. doi:10.1007/s00592-014-0562-6

Abstract

Whether metformin therapy affects bladder cancer risk in patients with type 2 diabetes mellitus (T2DM) has not been extensively investigated. The reimbursement databases of all Taiwanese patients with a new diagnosis of T2DM between 1998 and 2002 (n = 940,708) were retrieved from the National Health Insurance for follow-up of bladder cancer up to the end of 2009. Metformin was treated as a time-dependent variable, and of these patients, 532,519 were never-users and 408,189 were ever-users of metformin. A time-dependent approach was applied in the calculation of bladder cancer incidence and in the estimation of hazard ratios by Cox regression for ever-users, never-users, and subgroups of metformin exposure (using tertile cutoffs of cumulative duration of therapy and cumulative dose). During the study period, 1,847 (0.45 %) metformin ever-users and 6,213 (1.17 %) metformin never-users developed bladder cancer, representing an incidence of 72.03 and 189.22 per 100,000 person-years, respectively. The age-sex-adjusted and multivariable-adjusted hazard ratios (95 % confidence intervals) for ever- versus never-users were 0.382 (0.360–0.405) and 0.600 (0.564–0.638), respectively. The multivariable-adjusted hazard ratios for the first, second, and third tertiles of cumulative duration of metformin therapy were 1.034 (0.954–1.120), 0.696 (0.632–0.766), and 0.258 (0.229–0.291), respectively (P trend <0.0001). Similarly, the multivariable-adjusted hazard ratios for the first, second, and third tertiles of cumulative dose of metformin were 0.997 (0.920–1.080), 0.615 (0.559–0.677), and 0.285 (0.253–0.321), respectively (P trend <0.0001). This study suggests that metformin use is associated with a decreased risk of bladder cancer in patients with T2DM.

Keywords

Bladder cancerDiabetesEpidemiologyMetforminTaiwan

Copyright information

© Springer-Verlag Italia 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
  4. 4.Department of Internal MedicineNational Taiwan University HospitalTaipeiTaiwan