Metformin and survival of people with type 2 diabetes and pleural mesothelioma: A population-based retrospective cohort study

Abstract Objectives This study aimed to investigate the effect of metformin on survival of people with type 2 diabetes and pleural mesothelioma. Materials and methods We conducted a retrospective cohort study of people with type 2 diabetes diagnosed with pleural or unspecified mesothelioma between 1993 and 2014 using linked Scottish population-based diabetes and cancer datasets. Kaplan-Meier plots, log-rank tests, and Cox proportional hazards regression models were used to describe the association between use of metformin and all-cause mortality following diagnosis of pleural mesothelioma. Results There were 300 people with type 2 diabetes and pleural or unspecified mesothelioma of whom 148 had ever used metformin and 290 died during follow up. The median survival time was 8.8 months and 6.5 months for metformin users and non-users respectively ( p =0.37, log-rank test). After adjusting for age, sex, diabetes duration, socio-economic status, and other anti-diabetic medications the hazard ratio for mortality associated with metformin was 0.99 (95% confidence intervals: 0.76–1.28; p =0.92). Similar non-statistically significant associations were obtained in sensitivity analyses based on metformin use in year prior to diagnosis of mesothelioma, use of metformin for more than one year, in people below the mean age at diagnosis of mesothelioma (74 years) and 74 years of age or older, limitation to pleural mesothelioma and following further adjustment for body mass index and smoking. Conclusion There was no evidence that metformin improved survival among people with type 2 diabetes and pleural mesothelioma or to support trials of metformin in people with mesothelioma.