Impact of Hashimoto Thyroiditis on Long-Term Outcomes in Differentiated Thyroid Carcinoma

Hashimoto thyroiditis (HT) coexists with differentiated thyroid carcinoma (DTC), particularly papillary thyroid carcinoma, in approximately 25% of cases. However, the impact of this association on DTC outcomes remains controversial. The aim of this study was to analyze the influence of Hashimoto thyroiditis on disease-specific survival (DSS) and recurrence-free survival (RFS) in DTC patients. Methods: A retrospective study conducted at our institution between 2007 and 2020 analyzed 707 DTC patients treated with surgery and/or I-131 therapy. Cox proportional hazards regression was used to identify independent predictors, including sex, age, tumor histology, HT status, and initial TNM stage. Results: Among 707 DTC patients, 628 (88.8%) had papillary cancer, 582 (82.3%) were female, 395 (55.9%) were <55 years old; HT coexisted in 137 (19.4%) patients. During follow-up, 23 (3.25%) developed recurrent disease; at last follow-up, 638 (90.2%) were alive. Initial distant metastases (p < 0.001) and higher T stage (p = 0.002) independently predicted worse DSS. For RFS, male sex (p = 0.015), higher T stage (p = 0.018), and lymph node involvement (p = 0.023) independently predicted an increased risk of recurrence. HT was not an independent predictor of DSS (HR 0.97, 95% CI 0.21–4.52; p = 0.964) or recurrence (HR 0.36, 95% CI 0.05–2.73; p = 0.322). Conclusions: Although Hashimoto thyroiditis was associated with favorable clinicopathological features, it was not independently associated with disease-specific or recurrence-free survival. Conventional staging parameters, particularly tumor stage, remain the principal determinants of prognosis in differentiated thyroid cancer.