Impact of metformin on survival outcome of esophageal squamous cell carcinomas patients undergoing surgical resection: a multicenter retrospective study

BACKGROUND: Diabetes mellitus is a recognized risk factor for esophageal squamous cell carcinomas (ESCC), and metformin is a recognized protective factor for some gastrointestinal tumors. But knowledge is limited regarding the effect of metformin on survival outcome of ESCC patients with type 2 diabetes mellitus (T2DM). We assessed the impact of post-diagnosis metformin use on overall survival (OS) and disease-free survival (DFS) in ESCC with T2DM undergoing surgical resection. METHODS: A retrospective analysis was performed on 3,523 patients with ESCC who met the study conditions after surgical resection. Log-rank and Cox regression models were used to evaluate the relationship between metformin and T2DM and ESCC survival rate, and adjusted according to age, gender, BMI, smoking, drinking and staging, et al. RESULTS: Among included ESCC patients, 619 were associated with type 2 diabetes, while the remaining 2,904 were not associated with type 2 diabetes. The 5-year OS (28.43%) of patients with T2DM was significantly lower than that of patients without T2DM (32.75%), P=0.037. DFS in 5 years were 27.30% (with T2DM) and 31.75% (without T2DM) (P=0.030), respectively. Compared with patients without T2DM, patients with T2DM presented worse OS [adjusted risk ratio (HR(adj)) =1.19] and DFS (HRadj =1.17; P<0.001). Among the 619 patients with type 2 diabetes, 485 were treated with metformin and 134 were not treated with metformin. Patients treated with metformin had significantly improved OS [adjusted risk ratio (HR(adj)) =0.89; P=0.031) and DFS (HR(adj) =0.90; P=0.013). CONCLUSIONS: T2DM was again associated with poorer survival in ESCC patients, and metformin may improve the prognosis of these patients.