"Copy number alteration" as the sole molecular finding of a Thyroseq test is more commonly seen in Hurthle cell neoplasms.

BACKGROUND: To better understand the molecular alterations associated with Hurthle cell lesions of the thyroid, we retrospectively reviewed the association of clonal DNA copy number alterations (CNAs) with fine needle aspiration (FNA) cytomorphology and surgical follow-up. METHODS: Hurthle cell type (HCT) and non-Hurthle cell type (NHCT) thyroid FNAs that were classified according to the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) as atypia of undetermined significance (AUS) and suspicious for a follicular neoplasm (SFN) with corresponding molecular testing performed by ThyroSeq v3 genomic classifier were compared to surgical follow-up. RESULTS: A total of 54 thyroid FNA cases were identified, distributed among the following categories: AUS-HCT (n = 15, 27.8%), SFN-HCT (n = 11, 20.4%), AUS-NHCT (n = 19, 35.2%), and SFN-NHCT (n = 9, 16.6%). The lesions classified as AUS-HCT and SFN-HCT showed a higher prevalence of CNAs (n = 10/26; 38.5%) compared to their NHCT counterparts (n = 3/28; 10.7%) (p < .03). Of the 42 patients (77.8%) with surgical follow-up, CNAs were more often seen in benign (n = 10/26, 38.5%) than malignant conditions (n = 1/16, 6.3%) (p < .03). CNAs were encountered in more lesions with Hurthle cell features on histologic examination (n = 8/14, 57.1%) than those without (n = 3/28, 10.7%) (p < .002). The presence of CNAs alone was seen only in benign adenomas and more commonly with Hurthle cell features (n = 5/7, 71.4%). CONCLUSION: In this study, CNAs were associated with Hurthle cell morphology on thyroid FNA and benign adenomas upon surgical follow-up. Therefore, if the only finding of a positive ThyroSeq v3 GC result is a CNA, conservative management can be considered if clinically indicated.