Hashimoto's thyroiditis (HT) is an important cause of hypothyroidism caused by autoimmune chronic lymphocytic thyroiditis. In order to attain a better understanding for use in treatment of papillary thyroid carcinoma (PTC) coexisting with HT, we conducted an analysis of the clinicopathologic features, as well as the importance of HT as a prognostic factor.

In this retrospective study, we analyzed 341 patients who were histopathologically diagnosed with PTC following surgery.

PTC coexisting with HT was observed in 19.6% (67 patients) of all PTC patients. A statistically significant gender difference was observed in the group with HT (two male vs. 65 female), with a higher positive rate of anti-thyroglobulin antibody and smaller tumor size, compared to the PTC group without HT. When tumor size increased, a lower coexistence rate of HT was observed. No significant differences were observed in multifocality, cervical lymph node (LN) metastasis, coexistence of benign nodule, and extent of LN dissection. However, frequency of extrathyroidal extension was significantly lower and total thyroidectomy rate was higher in the group with HT. TNM stage and AMES stage were similar in both groups; frequency of high MACIS score showed a significant decrease in the group with HT. The recurrence rate and disease- free survival in patients with PTC were not significantly affected by coexistence of HT.

We found a significant relationship with gender, extrathyroidal extension, and tumor size in PTC coexisting with HT. However, no significant differences in recurrence rate and disease-free survival were observed between groups. Therefore, coexistence in PTC could not be applicable as a prognostic factor of PTC.