The causal association between Hashimoto's thyroiditis (HT) and papillary thyroid cancer (PTC) remains controversial. This research attempted to analyze clinicopathological relationships between HT and PTC, and to determine what influence the former has on the latter.

We retrospectively reviewed 773 patients who underwent thyroid surgery with PTC. These patients were divided into two groups, coexistent HT group and PTC alone group, and the clinicopathologic data were analyzed.

Out of 773 patients, the coexistent HT group included 269/773 (34.8%) patients and the control group included 504/773 (65.2%) patients. In comparison of these two groups, there were no significant differences in age, extent of surgery, serum T3, Free T4, number of tumors, multifocality, tumor size, extrathyroidal extension, and lymph node metastasis. In sex, women were at the higher rate in coexistent HT group than in the control group (P=0.008). Serum TSH level was higher in the coexistent HT group (P<0.001). In addition, using the AMES scoring system, the coexistent HT group showed a significantly higher rate of low risk than the control group (P=0.048). Multivariate analysis showed no significant association between HT and lymph node metastasis (P=0.081, odds ratio=1.335; 95% CI, 0.965~1.847).

The rate of women and serum TSH level were higher in the coexistent HT group. In addition, the low-risk group showed the higher rate in the case of accompanying HT, and though the HT does not affect the lymph node metastasis but much more researches would be needed on that.