Association between adipokines and thyroid carcinoma: a meta-analysis of case-control studies

BACKGROUND: The incidence of thyroid carcinoma is increasing all over the world. Some studies have suggested that the change of adipokines expression can induce thyroid carcinoma. However, other studies have come to the opposite conclusion. Therefore, we studied the relationship between adipokines and thyroid carcinoma. METHODS: Databases—PubMed, Cochrane Library, SinoMed, CNKI, Wanfang, and clinical trial registries were searched. A meta-analysis was then performed through a fixed or random-effects model to calculate I values for heterogeneity analysis. RESULTS: Twenty-nine articles were finally included for analysis. The level of serum tumor necrosis factor-alpha (TNF-α) [standardized mean difference (SMD) =1.31, 95% confidence interval (95% CI): 0.35 to 2.28, I(2) = 98%, P = 0.008] and the ratio of TNF-α immunoreactivity in tissues [odds ratios (OR) =6.36, 95% CI: 1.92 to 21.05, I(2) = 66%, P = 0.002] in thyroid carcinoma are significantly higher than those in control. The serum interleukin-6 (IL-6) in patients with thyroid carcinoma is higher than that in control (SMD = 1.04, 95% CI: 0.40 to 1.67, I(2) = 96%, P = 0.001). There is no significant difference of the ratio of IL-6 immunoreactivity in tissues between carcinoma and control (OR = 1.23, 95% CI: 0.62 to 2.43, I(2) = 86%, P = 0.55). The ratio of leptin immunoreactivity in tissues is significantly associated with the risk of thyroid carcinoma (OR = 12.21, 95% CI: 3.36 to 44.40, I(2) = 85%, P < 0.00001). However, after analyzing the expression level of serum adiponectin in three studies, no significant difference is found between thyroid carcinoma and the control (P = 0.81). CONCLUSIONS: Adipokines (TNF-α, IL-6 and leptin) show a strong relationship between elevated concentrations (in serum and/or tissue) and thyroid carcinoma. However, the association between adiponectin and thyroid carcinoma needs further research.