Metformin may improve the prognosis of patients with bladder cancer but was not associated with decreasing its risk, according to a study published in Medicine.1

Previous studies have demonstrated that patients with type 2 diabetes treated with metformin have a lower incidence of various cancers and improved long-term oncologic outcomes compared with other therapies. The impact of metformin on the incidence and prognosis of bladder cancer however, requires further study.

For this systematic review and meta-analysis, researchers assessed the outcomes of 9 retrospective cohort studies encompassing 1,270,179 patients. Eligible studies evaluated the association between metformin use and bladder cancer incidence and various prognostic measures, such as progression-free survival (PFS) and overall survival (OS).

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Five studies involving 1,269,642 patient lives demonstrated that metformin use does not decrease the risk of bladder cancer (hazard ratio [HR], 0.82; 95% CI, 0.61-1.09; P =.17). A subgroup analysis based on ethnicity showed that metformin was significantly associated with decreased risk among Asian patients (HR, 0.62; 95% CI, 0.48-0.81; P <.01), but not among non-Asian patients (HR, 0.90; 95% CI, 0.79-1.08; P =.32).

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Four studies with a total of 537 patients showed that metformin intake significantly 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), and cancer-specific survival (HR, 0.57; 95% CI, 0.40-0.81; P =.002). No significant prolongations of OS were observed (HR, 0.83; 95% CI, 0.47-1.44; P =.50).

The authors concluded that “further clinical and mechanistic studies are still required to determine the precise role of metformin in the initiation and progression of bladder cancer.”


Hu J, Chen JB, Cui Y, et al. Association of metformin intake with bladder cancer risk and oncologic outcomes in type 2 diabetes mellitus patients: a systematic review and meta-analysis. Medicine. 2018;97(30):e11596.