The presence of Hürthle cells does not increase the risk of malignancy in most Bethesda categories in thyroid fine-needle aspirates.

BACKGROUND Hürthle cell/oncocytic change is commonly reported on thyroid fine needle aspiration (FNA) and may be considered an "atypical cell" by clinicians. This study aims to delineate the association between Hürthle cells in preoperative cytology and subsequent pathology of the indexed thyroid nodule and to report rates of malignancy. METHODS Retrospective review of records of 300 patients with Hürthle cell/oncocytic change on FNA and final surgical pathology at a tertiary referral center between 2000 and 2013 was performed and compared to a multi-institutional FNA cohort. The degree of Hürthle cell presence was correlated with histopathologic diagnoses. RESULTS In our Hürthle cell FNA group, Bethesda System for Reporting Thyroid Cytopathology categories (BSRTC) were: I (non-diagnostic) - 14 (4.7%); II (benign) - 113 (37.7%); III (atypia of undetermined significance/follicular lesion of undetermined significance) - 33 (11%); IV (follicular neoplasm/suspicious for a follicular neoplasm) - 125 (41.6%); V (suspicious for malignancy) -12 (4%); and VI (malignant)- 3 (1%). When categorized based on the degree of Hürthle cell change, our Hürthle cell FNA group, 59 (29%) were classified as mild, 13 (6%) moderate, and 131 (65%) predominant. When comparing our results with a multi-institutional FNA cohort (all with surgical confirmation), the presence of Hürthle cells was found to be associated with a lower risk of malignancy in all BSRTC categories, with a statistically significant difference in the BSRTC IV and V groups. The sole exception was when Hürthle cell presence was classified as predominant (defined as greater than 75% of the cellular population), the rate of malignancy was significantly elevated in FNAs interpreted as benign/Bethesda II. CONCLUSION Although Hürthle cells have been considered by clinicians as an "atypical cell" their presence does not increase the risk of malignancy within BSRTC categories overall. However, when predominant Hürthle cell change is present, the risk of malignancy is increased in the benign cytology/BSRTC category II.