Prevalence of Hashimoto's thyroiditis in papillary thyroid cancer and its association with aggressive characteristics.

Background: Hashimoto's thyroiditis (HT) has been associated with papillary thyroid cancer (PTC), yet whether the clinicopathological features of PTC are affected by HT remains unknown. The purpose of this study was to investigate the association of HT with clinicopathological features of PTC.

Methods: We conducted a multicenter cross-sectional study to retrospectively evaluate the association of HT with clinicopathological features of PTC in the central provinces of China. The association between HT with clinicopathological features of PTC (including pathological HT and clinical HT) was evaluated by logistic regression analysis.

Results: A total of 15,305 patients with PTC were enrolled to this study, with a median age of 42 years at diagnosis, including 11,465 women (74.9%) and 3,840 men (25.1%). The overall prevalence of HT in PTC patients was 22.9% (3,505/15,305). Compared with PTC patients without HT, pathological HT was a potential protective factor for several aggressive characteristics of PTC, including BRAF^V600E mutation (P<0.001), extrathyroidal extension (P=0.04), larger primary tumor size (P<0.001), advanced primary tumor stage (P<0.001), and the number of metastatic lymph nodes >5 (P=0.006), whereas this effect was not observed in clinical HT except for the BRAF^V600E mutation and bilateral tumors (P<0.001 for both). Notably, both pathological (P<0.001) and clinical HT (P=0.04) are potential risk factors for multifocal tumors.

Conclusions: PTC patients often have concomitant HT. Some potential links between the 2 entities are present. Pathological HT is a potential protective factor for some aggressive characteristics of PTC, whereas this effect does not present in clinical HT, which has guiding significance for clinical treatment decision-making.