Does the Association of Hashimoto's Thyroiditis with Differentiated Thyroid Cancer Really Have a Protective Role?

The study is an investigation of aggressive tumor features, prognosis, and disease-specific mortality rates of differentiated thyroid cancer (DTC) in the presence of concomitant Hashimoto's Thyroiditis (HT). The data of patients with DTC followed in our tertiary care center between 2000-2022 were analyzed. Variables such as patient age, gender, preoperative serum autoantibody levels, tumor characteristics, and treatment modalities were obtained from medical records. The diagnosis of HT was based either on the presence of a positive result in the pathological examination and/or on antibody positivity. A total of 637 patients [mean±SD age, 44.9±13.5 years; 485 women [76.1%)] were included in the analysis. The overall prevalence of coexistent HT was 22.9% (n=146). The disease-specific mortality associated with DTC was 2.9%. DTC patients with HT compared to those without; have more positive lymphovascular invasion (p<0.001), and lymph node metastases (p<0.001). According to the Kaplan-Meier curves, disease-specific survival rates among DTC patients without HT were significantly higher than patients with HT (log-rank p=0.002). The disease-specific mortality rate was 4.79% in DTC patients with HT, it was 1.43% in those without HT. Hashimoto thyroiditis was not associated with a 10-year recurrence-free survival (p=0.059). Differentiated thyroid cancers with concomitant HT are associated with some aggressive tumor features (such as lymphovascular invasion and nodal metastasis) and lower survival. In staging systems based on tumor risk factors, it may be useful to evaluate the presence of concomitant HT as a prognostic factor.