Risk of bladder cancer in patients with type 2 diabetes mellitus: a retrospective population-based cohort study in Lithuania

Purpose The objective of our study was to evaluate bladder cancer risk among Lithuanian type 2 diabetes mellitus (T2DM) patients and the effect of antihyperglycemic therapy on bladder cancer risk. Methods We analyzed bladder cancer risk in a cohort of patients who were diagnosed with T2DM between 2001 and 2012 in Lithuania. Bladder cancer risk in four groups of antihyperglycemic medication users (insulin-only, metformin-only, sulfonylurea-only, and pioglitazone +/- any other drug) was also assessed. Standardized incidence ratios for bladder cancer were calculated. Results A total of 76,818 patients (28,762 males and 48,056 females) with T2DM were included in the final cohort. In the whole cohort of diabetic patients, 277 bladder cancer cases were observed, compared to 232.75 expected cases, according to bladder cancer rates in the general population (Standardized Incidence Ratio 1.19; 95% Confidence Interval: 1.06-1.34). Higher risk of bladder cancer was found in both men and women; however, in women the risk increase was not statistically significant. We found higher risk of bladder cancer in patients of both sexes diagnosed with T2DM at the age of 50-79 years and also in all groups of different antihyperglycemic medication users. Conclusion T2DM was associated with increased risk of bladder cancer.