Does papillary thyroid carcinoma have a better prognosis with or without Hashimoto thyroiditis?

Background: It has been reported that the BRAF^V600E mutation is related to a low frequency of background Hashimoto thyroiditis (HT); however, there are not many factors known to be related to the development of HT. The aim of this study was to determine whether patients with both papillary thyroid carcinoma (PTC) and HT show aggressive features, by investigating the clinicopathological features of HT in patients with PTC. Methods: A database of patients with PTC who underwent thyroidectomy between October 2008 and August 2012 was collected and reviewed. All 2464 patients were offered a thyroidectomy, and DNA was extracted from the atypical cells in the surgical specimens for detection of the BRAF^V600E mutation. Clinical and pathological characteristics were also investigated. Results: Four hundred and fifty-two of 1945 (23.2 %) patients were diagnosed with HT, and of these, 119 (72.1 %) had a BRAF^V600E mutation. HT was not significantly associated with the BRAF^V600E mutation (P < 0.001) and extrathyroidal extensions (P = 0.005) but was associated with a low stage (P = 0.011) and female predominance (P < 0.001). In a subgroup analysis for gender, HT was associated with a low probability of BRAF^V600E mutations in both genders (P < 0.001 for both females and males). Also, recurrence was significantly associated with HT (OR 0.297, CI 0.099–0.890, P = 0.030), lymph node ratio (OR 2.545, CI 1.092–5.931, P = 0.030), and BRAF^V600E mutation (OR 2.075, CI 1.021–4.217, P = 0.044). However, there was no relationship with clinicopathological factors or with death. Conclusions: Our results show that HT in patients with PTC is associated with a low probability of BRAF^V600E mutations. Moreover, HT was correlated with some factors that were associated with less aggressive clinical features and inversely related to recurrence. Therefore, these results may be useful to predict whether PTC concurrent with HT exhibits a better prognosis than PTC alone.