What is known and objective: Metformin has been suggested to confer anticancer efficacy. However, it remains uncertain whether additional use of metformin could improve survival of women with breast cancer. We performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the influence of metformin on survival outcome in women with breast cancer.
Methods: Relevant RCTs were obtained by search of PubMed, Embase and Cochrane's Library databases from inception to 15 May 2021. A random-effects model incorporating the potential publication bias was used to pool the results.
Results and discussion: Five phase II RCTs including 396 non-diabetic women with breast cancer were included in the meta-analysis. Pooled results showed that additional use of metformin was not associated with improved progression-free survival (PFS, hazard ratio [HR]: 1.00, 95% confidence interval [CI]: 0.70 to 1.43, p = 0.98; I2 = 32%) or overall survival (OS, HR: 1.00, 95% CI: 0.71 to 1.39, p = 0.98; I2 = 0%). Sensitivity analysis by excluding one study at a time showed consistent results (HR for PFS: 0.91 to 1.14, p all >0.05; HR for OS: 0.88 to 1.21, P all >0.05).
What is new and conclusion: Current evidence from phase II clinical trials does not support that additional use of metformin could improve the survival outcome in women with breast cancer.
Keywords: breast cancer; meta-analysis; metformin; randomized controlled trials; survival.
© 2021 John Wiley & Sons Ltd.