The association between metformin and ovarian cancer survival: a systematic review and meta-analysis of cohort studies.

Background: A number of observational studies examined the association between metformin therapy and ovarian cancer survival outcomes, but the results are inconsistent. Objective: The study aimed to investigate the effect of metformin on survival for ovarian cancer patients. Method: PubMed, Embase and Web of Science databases were searched for relevant studies from the inception to June 11, 2019. The strength of the relationship was assessed using summary of hazard ratios (HRs) with corresponding 95% confidence intervals (CI). Statistical analyses were carried out using the random-effects model. Results: Totally, 6 retrospective cohort studies involving 2,638 ovarian cancer patients were included. Metformin was not associated with improved overall survival (HR=0.78, 95% CI 0.54-1.12, P=0.175, I-2 = 61.6%) and disease-free survival (HR=0.49, 95% CI 0.20-1.17, P=0.106, I-2=82.1%) in ovarian cancer patients compared to non-metformin users. Conclusion: The current study provides preliminary evidence that metformin may not be associated with a survival benefit for ovarian cancer patients. More studies with rigorous designs are needed.