Thyroid cancer and Hashimoto's thyroiditis in AUS/FLUS nodules: is there a correlation? A retrospective study

The global prevalence of Hashimoto's thyroiditis (HT) and differentiated thyroid cancer (DTC), particularly papillary thyroid cancer (PTC), is increasing. However, studies assessing correlations between these diseases have yielded inconsistent findings. Furthermore, patients diagnosed with HT show a higher prevalence of indeterminate cytology than those without HT. This study was aimed at assessing the interaction between HT and DTC in patients undergoing thyroidectomy for indeterminate thyroid nodules (ITNs), and investigating the role of repeated fine-needle aspiration cytology (FNAC) in ITNs with HT.

This retrospective study enrolled 111 consecutive patients who underwent thyroidectomy for ITNs over a 4-year period. The outcome measures included demographic information; numbers and diagnoses of FNAC; risk of malignancy; serum thyroid-stimulating hormone levels; ultrasound features; and features of aggressiveness, including lymphovascular invasion, extrathyroidal extension and lymph node metastasis.

Among the participants, 76.6 % were women, and 46.8 % had malignant pathology. Overall, HT did not increase malignancy risk, according to the final histopathology. However, the presence of HT significantly increased the probability of a PTC diagnosis with repeated FNAC (odds ratio = 9.3; 95 % confidence interval: 1.0-96.3). Furthermore, significant correlations were observed between malignant nodules with HT and age, sex, lymph node metastasis and positive margins.

Overall, HT did not increase malignancy risk in the final pathology of ITNs but did increase the risk of a cytological PTC diagnosis with repeated FNAC. Because this study was based in a local community setting, large, collaborative, multicenter studies are required to validate our findings.