Hashimoto's thyroiditis as a risk factor of papillary thyroid cancer may improve cancer prognosis.

Objective: Hashimoto's thyroiditis (HT) has been associated with an elevated risk of papillary thyroid cancer (PTC). To investigate the possible influence of HT on the prognosis of PTC patients, we assessed the related clinical factors linking these conditions, especially serum thyroid-stimulating hormone (TSH) concentration.

Study Design: Case-control study.

Setting: The First Hospital of China Medical University.

Subjects And Methods: The demographic and histological characteristics of 2478 patients who underwent thyroidectomy at our center from 2004 to 2012 were analyzed.

Results: Compared with patients with benign thyroid nodular disease, patients with PTC showed a significantly higher prevalence of HT (18.8% vs 7.2%, P < .001), mean TSH concentrations (2.02 ± 1.76 vs 1.46 ± 1.21 mIU/L, P < .001), and positivity rates for anti-thyroglobulin antibodies (TGAB; 40.0% vs 20.4%, P < .001) and anti-thyroid peroxidase antibodies (24.8% vs 12.5%, P < .001). These differences remained after excluding all HT patients. The TSH concentrations were significantly higher in PTC patients with HT than in those without HT (2.54 ± 2.06 vs 1.90 ± 1.66 mIU/L, P = .001). Patients with PTC and HT were younger, with a female predominance, and had smaller sized tumors with less advanced TNM stage compared with those without HT, indicating a better prognosis. Multivariate analysis showed that HT, higher TSH concentration, male sex, and TGAB positivity were independent risk factors for PTC development.

Conclusion: Histologically confirmed HT is associated with a significantly higher risk of PTC, due primarily to the higher serum TSH concentrations resulting from the tendency to hypothyroidism in HT. Autoimmunity is another independent risk factor for PTC but may be associated with a better prognosis.