Persistent organic pollutants, pesticides, and the risk of thyroid cancer: systematic review and meta-analysis.

Previous epidemiological studies have reported persistent organic pollutants (POPs) and some nonpersistent pesticides and the risk of thyroid cancer. The aim of this study was to assess the association between exposure to POPs, pesticides, and thyroid cancer by carrying out a meta-analysis. Literature searches were performed using PubMed, Embase, and reference lists of relevant articles. Summary risk estimates for thyroid cancer were calculated using fixed-effects and random-effects models. In addition, several subgroup and sensitivity analyses were carried out. Fifteen studies were reviewed, and eight studies were included in the meta-analysis. Pesticide exposure showed positive, statistically significant associations with thyroid cancer [odds ratio (OR)=1.48, 95% confidence interval (CI)=1.15-1.91, I=48%, Pheterogenetiy=0.05]. After subgroup analysis, herbicide exposure (OR=3.00, 95% CI=1.38-6.54) and agricultural exposure to pesticides (OR=1.86, 95% CI=1.04-3.32) was associated with an increased risk of thyroid cancer. A sensitivity analysis showed that the results were robust. Exposure to pesticides was associated with an increased risk of thyroid cancer in this meta-analysis. Future studies should investigate exposure to POPs or pesticides with controls for potential confounders using biological samples.