Association between prediabetes and thyroid cancer risk: A meta-analysis

Prediabetes, characterized by intermediate hyperglycemia, is increasingly prevalent worldwide. While diabetes has been associated with a heightened risk of various cancers, the relationship between prediabetes and thyroid cancer remains ambiguous. This meta-analysis sought to assess whether prediabetes correlates with an elevated incidence of thyroid cancer. A systematic literature search was conducted across PubMed, Embase, Web of Science, Wanfang, and CNKI to identify longitudinal studies that compared the incidence of thyroid cancer in individuals with prediabetes to those with normoglycemia. Risk ratios (RRs) with 95% confidence intervals (CIs) were aggregated using a random-effects model. Subgroup and sensitivity analyses were performed to identify potential effect modifiers. Six prospective cohort studies, encompassing 5,743,849 participants, were included in the analysis. Overall, prediabetes was not significantly correlated with thyroid cancer incidence (RR = 1.04; 95% CI: 0.98-1.11; p = 0.23; I² = 53%). Subgroup analyses revealed no significant variations based on age, sex, region, follow-up duration, or definition of prediabetes. Notably, a significant association was identified in studies utilizing cancer registries or validated clinical diagnoses (RR = 1.29; 95% CI: 1.04-1.60), in contrast to studies relying solely on ICD-10 codes (RR = 1.01; 95% CI: 0.98-1.05; p for subgroup difference = 0.03). In conclusion, prediabetes was not linked to a significantly increased risk of thyroid cancer overall. However, a potential association was noted in studies employing clinically validated cancer diagnoses. These findings, derived from observational cohorts, should be interpreted cautiously, and further prospective research is necessary to elucidate any causal relationship.