Endocrine Abstracts

Background: Whether metformin therapy affects bladder cancer risk in patients with type 2 diabetes mellitus (T2DM) has not been extensively investigated.

Methods: The reimbursement databases of all Taiwanese patients with a new diagnosis of T2DM between 1998 and 2002 (n=940708) were retrieved from the National Health Insurance for follow-up of bladder cancer up to the end of 2009. Of these patients, 532519 were never-users and 408189 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.

Results: During the study period, 1874 (0.45%) metformin ever-users and 6213 (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- vs never-users were 0.335 (0.256–0.437) 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) 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) cumulative dose of metformin.

Conclusions: Metformin use is associated with a decreased risk of bladder cancer.