Context: Hashimoto's thyroiditis (HT) can be divided into IgG4-positive and IgG4-negative HT. The potential association between IgG4-positive HT and papillary thyroid carcinoma (PTC) remains poorly understood.
Objective: The aim was to investigate the relationship between IgG4-positive HT and PTC and to compare the prognostic parameters of PTC patients with and without IgG4-positive HT.
Design: This was a retrospective study.
Patients and setting: A total of 66 HT patients (18 HT-alone, 48 HT with PTC) with serum samples stored before the operation were collected. Another 18 PTC-alone patients were collected as controls.
Main outcomes: Expression of IgG4, IgG, and TGF-β1 in thyroid tissues and serum levels of IgG4, TgAb IgG, TgAb IgG4, TPOAb IgG, and TPOAb IgG4 were measured.
Results: Seventeen HT patients with PTC (35.4%) were IgG4-positive HT, whereas only one patient (5.6%) was found to be IgG4-positive in the HT-alone group. In contrast, there were only a few IgG4-positive plasma cells in the PTC-alone group. The association of IgG4-positive HT and PTC was statistically significant (P < .05). Moreover, serum levels of TgAb IgG4 and the ratios of TgAb IgG4 to TgAb IgG were significantly higher in the HT with PTC and the PTC-alone groups than in the HT-alone group (P < .05). Furthermore, in the HT with PTC group, the average tumor diameter of 17 IgG4-positive HT with PTC patients was 1.7 ± 0.8 cm, whereas of 31 IgG4-negative HT patients with PTC, the diameter was 1.2 ± 0.6 cm (P = .01). A considerably higher percentage of lymph node metastasis (41.2% vs 12.9%; P = .026) was found in PTC patients with IgG4-positive HT as compared with those with IgG4-negative HT.
Conclusion: PTC may be facilitated by preexisting autoimmune inflammation of IgG4-positive HT. IgG4-positive HT with PTC cases may have worse clinical outcomes. The high levels of TgAb IgG4 might present a risk factor for PTC.