Metformin Use Is Associated With Better Survival of Breast Cancer Patients With Diabetes: A Meta-Analysis

Background. Diabetic patients with breast cancer receiving metformin and neoadjuvant chemotherapy have a higher pathologic complete response rate than do diabetic patients not receiving metformin, but findings on salvage treatment have been inconsistent. We performed a meta-analysis to assess the effect of adding metformin to standard therapy on the prognosis of breast cancer patients with diabetes. Methods. We searched PubMed, Embase, Web of Science (Thomson Scientific), China Knowledge Resource Integrated Database, VIP journal integration platform, and chineseBioMedical Literature Database from inception to January 10, 2015, without language restrictions, including references related to metformin, breast cancer, and prognosis. We performed the meta-analysis using a random-effects model, with hazard ratios (HRs) and 95% confidence intervals (95% CIs) as effect measures. Results. A total of 11 studies consisting of 5,464 breast cancer patients with diabetes were included, comprising 2,760 patients who had received metformin and 2,704 patients who had not. Themeta-analysis showed that metformin was associated with better overall survival times (HR: 0.53; 95% CI: 0.39-0.71) and cancer-specific survival times (HR: 0.89; 95% CI: 0.79-1.00). Subgroup analysis revealed that metformin improved the overall survival by 65% after adjusting for hormone receptor expression (HR: 0.35; 95% CI: 0.15-0.84). Taking metformin after the diagnosis of breast cancer was still associated with prolonged overall survival. Conclusion. The use of metformin in standard cancer therapy might improve both overall and cancer-specific survivals of diabetic patients with breast cancer.