Hashimoto's Thyroiditis is an Important Risk Factor of Papillary Thyroid Microcarcinoma in Younger Adults.

The association between autoimmune thyroid disease and thyroid cancer remains unclear. We performed a matched case-control study to assess the association between Hashimoto's thyroiditis and papillary thyroid microcarcinoma (PTMC). A total of 927 PTMC cases and 927 age- and gender- matched controls selected from the same population were recruited. Odds ratio (OR) with 95% confidence interval (95% CI) was used to assess the strength of the association between Hashimoto's thyroiditis and PTMC. Conditional logistic regression analysis was carried out, and stratified analyses by age, gender and types of thyroid antibodies were also performed. Hashimoto's thyroiditis was significantly associated with increased risk of PTMC (OR=1.87, 95% CI 1.49-2.34, p<0.001). Stratified analysis by thyroid antibodies also found obvious associations of PTMC risk with TPOAb positivity (OR=1.58, p=0.001) and TGAb positivity (OR=2.35, p<0.001). Stratified analyses by age showed that the association between Hashimoto's thyroiditis and PTMC risk was more significant in younger adults aged between 18 and 30 years (OR=11.48, p<0.001). Further stratified analyses by thyroid antibodies also found that the associations of PTMC risk with TPOAb positivity or TGAb positivity were more significant in younger adults aged between 18 and 30, and the ORs were 8.27 (p<0.001) and 12.71 (p<0.001), respectively. This study suggests an obvious relationship between Hashimoto's thyroiditis and PTMC risk, and Hashimoto's thyroiditis is an important risk of PTMC in younger adults.