Clinical relationship between Hashimoto's thyroiditis and papillary thyroid cancer

The relationship between Hashimoto's thyroiditis (HT) and papillary thyroid cancer (PTC) with regard to their co-occurrence and the effect of concurrent HT on the prognosis of PTC has been debated. The aim of the present study is to determine a clinical relationship between these two disease entities and to evaluate the correlation between concurrent HT and various clinicopathological parameters.

Demographic and histopathological data were collected from 675 patients undergoing thyroid surgery from 2000 to 2005, and 303 patients who received initial treatment for thyroid disease at our institution and whose medical records were accessible for review were enrolled in this study. Of these participants, 269 with histologically confirmed PTC were analysed according to the presence or absence of concurrent HT.

Of 269 patients with PTC, 21.6% (58/269) had concurrent HT, whereas only 5.9% (2/34) had concurrent HT with another diagnosis (p = 0.031, odds ratio = 4.4; 95% CI, 1.02-18.90). Younger age at presentation and a greater female preponderance were noted in patients with HT compared with those without HT (p = 0.008 and p = 0.009, respectively). Although it was not statistically significant, PTC with HT patients tented to have smaller tumour size (1.6 ± 1.0 cm vs. 1.8 ± 1.5 cm), lower incidence of lymph node metastasis at presentation (12.2% vs. 29.9%), unifocal disease (84.5% vs. 78.7%), and early-stage disease. Additionally, PTC with HT patients exhibited better prognosis, viewed in recurrence and mortality, during the 62-month mean follow-up period.

HT was definitely associated with PTC as was chronic inflammation with cancer in other locations. Interestingly, however, the coexistence of HT in PTC cases introduced favourable clinical outcomes compared with those of PTC without HT.