**4.1 Bladder cancer**

A review of 9 retrospective cohort studies with 1,270,179 patients did not reveal a benefit from metformin in preventing bladder cancer (Hazard ratio (HR) = 0.82, 95% CI = 0.61–1.09; *P* = .17). However, metformin intake was associated with an improved recurrence-free survival (HR = 0.55, 95% CI = 0.35–0.88; *P* = .01), progression-free survival (HR = 0.70, 95% CI = 0.51–0.96; *P* = .03), as well as cancer-specific survival (HR = 0.57, 95% CI = 0.40–0.81; *P* = .002) [72].
