Autoimmune thyroiditis in paediatric thyroid cancer: clinical features and outcomes

To evaluate clinical characteristics and survival outcomes of paediatric differentiated thyroid carcinoma (paedDTC) in patients with and without autoimmune thyroiditis (AIT).

Retrospective cohort analysis of paedDTC patients with and without AIT, prospectively enrolled in the German Malignant Endocrine Tumour Registry between 1997 and 2024.

We analysed data from paediatric patients (<18 years) with histopathologically confirmed DTC, stratified by AIT status. Variables included demographics, tumour characteristics, lymph node involvement, and metastasis. Survival outcomes were assessed using Kaplan-Meier estimates.

Among 401 evaluable patients, 16.0% had AIT. AIT patients were significantly older at diagnosis (P < .001) and showed a non-significant tendency toward higher female predominance (P = .098). Patients with AIT demonstrated significantly lower rates of distant metastasis (7.5% vs. 22.2%, P = .014) compared with those without AIT. No significant differences were observed in tumour size, capsule invasion, lymphatic or vascular invasion, soft tissue infiltration, or multifocality. A tendency toward improved event-free survival (EFS) was observed in AIT patients (87.5% vs. 72.1%, P = .255), while overall survival (OS) was comparable (91.8% vs. 86.0%, P = .167) during the study period. Among patients with known AIT history, paedDTC was significantly more frequently diagnosed through surveillance compared with non-AIT patients (44.2% vs. 28.3%, P = .022).

AIT was present in 16% of paedDTC patients and was associated with reduced distant metastasis. A tendency toward improved EFS but similar OS during the follow-up period was observed. Earlier detection through surveillance in AIT patients may contribute to these findings, warranting further investigation into underlying biological mechanisms.