LAUSR

Although neurotrophin tyrosine receptor kinase (NTRK)– rearranged thyroid carcinoma (NRTC) is uncommon, its possible aggressive behavior and the availability of targeted therapies make its recognition relevant. We read with interest the first cytomorphologic characterizations of NRTC in recent articles by Abi-Raad et al and Viswanathan et al, and we aim to supplement those reports. These author groups retrospectively reviewed cytologic specimens/reports corresponding to surgically resected NRTC, including fine-needle aspiration (FNA) specimens from 13 and 19 patients, respectively. Both groups identified mixed architectural patterns (including microfollicular, crowded, or loosely cohesive groups and single cells) and tumor cells with distinctive oncocytic/vacuolated cytoplasm as characteristic. Findings diverged regarding background fibrosis and chronic lymphocytic thyroiditis, with each feature observed in nearly all of one cohort and in none of the other. Most FNAs (72% [13 of 18]) were classified as malignant in one cohort, whereas 23% (3 of 13) were classified as malignant in the other. We identified 4 FNAs from 4 female patients aged 29 to 91 years. Genetic alterations included ETV6-NTRK3 (n = 2), EML4-NTRK3 (n = 1), and TPR-NTRK1