Malignancy risk in indeterminate thyroid nodules with Hürthle cells: role of autoimmune thyroiditis.

Introduction Hurthle cells are modified follicular thyroid cells, whose development and proliferation have been related to different stimuli inducing cellular stress. Most thyroid aspirates containing Hurthle cells are classified as indeterminate, although the specific risk of malignancy for this subtype of atypia remains unclear. The aim of our study was to assess if the presence of Hurthle cells in indeterminate thyroid nodules correlates with the risk of malignancy. We further evaluated if this risk can be modified by the presence of an underlying Hashimoto's thyroiditis. Materials and methods We retrospectively analyzed all indeterminate thyroid nodules that were surgically treated at our institution between January 2010 and March 2019. For each nodule, we inferred the presence of Hurthle cells in the cytological report. Cytological findings were then correlated with histological reports. Results 354 indeterminate thyroid nodules were included in the study. The rate of malignancy resulted significantly lower in nodules exhibiting Hurthle cells compared to those negative for this cellular pattern (11.4% vs 22.5%, p = 0.01). Although there was no difference in the rate of malignancy in the whole population according to the presence or absence of Hashimoto's thyroiditis (21.5 vs 18.5%, p = 0.63), the significantly lower prevalence of malignant lesions in nodules with Hurthle cells was confirmed only in the presence of a histologically documented Hashimoto's thyroiditis (6.2% vs 32%, p = 0.005). Conclusions The finding of Hurthle cells in indeterminate thyroid nodules is associated with a low risk of malignancy in patients with an underlying Hashimoto's thyroiditis. The clinical management of these lesions may therefore be more conservative.