Endocrine Abstracts

Introduction: Coexistence of autoimmune thyroiditis (AIT) and papillary thyroid cancer (PTC) has been well documented, but causality is still a matter of debate. Pathogenetic links between PTC and AIT try to explain two theories: 1) PTC is induced or facilitated by AIT, 2) AIT is a response to PTC. It is believed that PTC associated to AIT has a better prognosis.

Aims: To find out: 1) the incidence of AIT in PTC patients, 2) the course of PTC associated to AIT, 3) relationship between these diseases.

Methods: Histological and laboratory results of 1251 differentiated thyroid cancer (DTC) patients were reviewed. 90% of them were PTC patients. Diagnosis of AIT was based on histological finding and/or high antiTPO level (≥ 3-times above upper reference range limit).

Results: The incidence of AIT in DTC/PTC patients was 41% (four-times higher compared to general population). PTC patients with coexisting AIT compared to that without AIT had better prognostic indicators (TNM), e.g. significantly higher incidence of micro- and small cancers (T1) and lower incidence of distant metastases. These illusory favourable findings were caused by the fact, that 65% of AIT patients were followed-up for this disease and PTC developed and was revealed during this period. When we compared prognostic indicators of PTC patients without AIT with those of PTC patients where AIT was revealed only after operation, no significant difference were found out. AIT therefore does not improve the clinical course of PTC patients.

Conclusions: We detected a high incidence of AIT in PTC patients. These data support the hypothesis that AIT is a predisposing factor in the development of PTC. Clinicians should pay particular attention to thyroid nodules in AIT. AIT does not represent a protective factor against spreading of PTC. At first sight better prognosis of PTC with coexisting AIT is not caused by immunological mechanisms, but by follow-up of AIT patients and therefore timely diagnosis of PTC.