AbstractBackgroundIt is unclear how diabetes and metformin use is associated with survival of esophageal cancer.MethodsThis population-based cohort study included new cases of esophageal cancer reported in Sweden from 2006 to 2018 with follow-up through 2019. Diabetes status and metformin use were analyzed in relation to all-cause and disease-specific mortality using multivariable Cox regression. The hazard ratios (HRs) with 95% confidence intervals (CIs) were adjusted for age, sex, calendar year, obesity, comorbidity, and use of nonsteroidal anti-inflammatory drugs or statins. For comparison reasons, 3 other antidiabetic medications were also analyzed (ie, sulfonylureas, insulin, and thiazolidinedione).ResultsAmong 4851 esophageal cancer patients (8404 person-years), 4072 (84%) died during follow-up. Compared with esophageal cancer patients with diabetes but not using metformin, decreased all-cause mortality was indicated among nondiabetic patients (without metformin) (HR = 0.86, 95% CI = 0.77 to 0.96) and diabetic patients who used metformin (HR = 0.86, 95% CI = 0.75 to 1.00). The hazard ratios of all-cause mortality decreased with a higher daily dose of metformin (Ptrend= .04). The corresponding hazard ratios for disease-specific mortality were similar but slightly attenuated. The results were also similar in separate analyses of esophageal cancer patients with adenocarcinoma or squamous cell carcinoma, with tumor stage I-II or III-IV, and in those who had or had not undergone surgery. No associations with mortality outcomes were found for use of sulfonylureas, insulin, or thiazolidinedione.ConclusionsDiabetes was associated with an increased all-cause mortality, whereas metformin use was associated with decreased all-cause mortality among esophageal cancer patients. More research is needed to determine if metformin affects survival in esophageal cancer.