Type 2 diabetes mellitus and risk of malignant melanoma: a systematic review and meta-analysis of cohort studies

Epidemiology studies have demonstrated inconsistent associations between type 2 diabetes mellitus and the risk of malignant melanoma. To this end, the aim was to perform a meta-analysis of cohort studies. Medline, PubMed, Embase and the Cochrane Library were searched up to February 2014. Cohort studies addressing the relative risk of type 2 diabetes mellitus on malignant melanoma were included in this meta-analysis. The Newcastle-Ottawa Scale was applied for quality evaluation. The pooled relative risks with the corresponding 95% confidence intervals (95% CIs) were calculated by using random-effects or random-effects model. Heterogeneity and publication bias were evaluated by I (2) and funnel plot analysis, respectively. Data was analyzed using STATA 11.0. A total of 9 independent cohorts from 8 manuscripts were entered this meta-analysis. Type 2 diabetes mellitus was slightly associated with an increased risk of malignant melanoma, and the pooled relative risk was 1.15 (95% CI, 1.00-1.32) in diabetes compared with non-diabetes with significant evidence of heterogeneity among these studies (P=0.016, I (2) =57.6%). For the studies adjusted for age, gender and obesity, the relative risks were 1.21 (95% CI, 1.03-1.42), 1.17 (95% CI, 1.01-1.35) and 1.11 (95% CI, 1.00-1.24), respectively. For the population-based studies in which case cohort established, the relative risk was 1.85 (95% CI, 1.31-2.62). Type 2 diabetes might be an independent risk factor for malignant melanoma. Further studies are needed to specifically test the effect, and fully elucidate the underlying pathophysiologic mechanisms.