Diabetes mellitus, metformin and head and neck cancer.

INTRODUCTION: Diabetes mellitus (DM (Diabetes Mellitus)) is directly associated with some cancers. However, studies on the association between diabetes mellitus and head and neck cancer (HNC (Head and Neck Cancer)) have rendered controversial results. The objective of this study was to evaluate the association between DM and HNC, as well as the impact of metformin use on the risk of HNC. MATERIAL AND METHODS: This case-control study was conducted within the framework of the Brazilian Head and Neck Genome Project in 2011-2014. The study included 1021 HNC cases with histologically confirmed squamous cell carcinoma of the head and neck admitted to five large hospitals in São Paulo state. A total of 1063 controls were selected in the same hospitals. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using unconditional logistic regression. RESULTS: Diabetic participants had a decreased risk of HNC (OR=0.68; 95% CI: 0.49-0.95) than non-diabetic participants, and this risk was further decreased among diabetic metformin users (OR=0.54; 95% CI: 0.29-0.99). Diabetic metformin users that were current smokers (OR=0.13; 95% CI: 0.04-0.44) or had an alcohol consumption of >40g/day (OR=0.31; 95% CI: 0.11-0.88) had lower risk of HNC than equivalent non-diabetic participants. CONCLUSION: The risk of HNC was decreased among diabetic participants; metformin use may at least partially explain this inverse association.