Type 2 diabetes mellitus and risk of head and neck cancer subtypes: a systematic review and meta-analysis of observational studies.

Aims: The association between type 2 diabetes mellitus (T2DM) and risk of head and neck cancer (HNC) remains unclear. This study aims to perform a system review and meta-analysis to explore this relationship. Methods: PubMed, Web of Science, and Embase databases were searched for studies published up to July 31, 2020, regarding the association between T2DM and HNC risk. A random-effects model was utilized to calculate summary relative risks (RRs) with corresponding 95% confidence intervals (CIs). Results: Fourteen case–control studies and thirteen cohort studies were included in our analysis. We observed a weak association between T2DM and risk of HNC overall, but there was no statistical significance (RR, 1.04; 95% CI, 0.88–1.23; I2 = 83.2%). Interestingly, there was a strong association in East Asia (RR, 1.46; 95% CI, 1.21-1.77; I2 = 36.6%). For HNC subtypes, T2DM conferred a significantly elevated risk in oral cancer (RR, 1.22; 95% CI, 1.01–1.47; I2 = 89.0%). However, in subgroup analyses of smoking, alcohol use, and body mass index (BMI)/obesity adjustments, the association between T2DM and oral cancer risk became insignificant. In addition, T2DM was not associated with a statistically elevated risk of pharyngeal cancer (RR, 1.18; 95% CI, 0.94–1.49; I2 = 72.9%) and laryngeal cancer (RR, 1.03; 95% CI, 0.88–1.22; I2 = 71.2%). Conclusions: This meta-analysis indicates that T2DM is associated with an increased risk of HNC in East Asia. As for site-specific cancer types, the risk of oral cancer was significantly increased in T2DM patients, which appear to be mediated or confounded by smoking, alcohol use, or BMI/obesity. [ABSTRACT FROM AUTHOR]