Genetic heterogeneity of indeterminate thyroid nodules assessed preoperatively with next-generation sequencing reflects the diversity of the final histopathologic diagnosis.

Introduction: Inconclusive cytologic results of thyroid fine‑needle aspiration biopsy (FNAB) include atypia or follicular lesion of undetermined significance (FLUS) and follicular neoplasm or suspicious for follicular neoplasm (SFN).

Objectives: We aimed to assess the genetic background of indeterminate thyroid nodules and to identify new genetic pathways potentially involved in the development of follicular thyroid cancer.

Patients And Methods: Genomic DNA was isolated from FNAB samples from 25 white patients (2 men; 23 women) diagnosed preoperatively with FLUS (n = 16) and SFN (n = 9). Next‑generation sequencing (NGS) was performed. The results were compared with clinical data, including final postsurgical diagnoses.

Results: The malignancy rate was 28%. KDR, RET, and TP53 gene mutations were most frequent in FLUS and SFN samples finally diagnosed as cancers, whereas alterations in RET, TP53, FLT3, APC, and PDGFRA predominated in benign tumors. KDR tended to be more common in malignant samples (75% vs 20%, P = 0.1). A total number of mutated genes was higher in patients with benign tumors (17 vs 11, P = 0.02), but there was no difference between groups in the mean number of mutations per patient (4.9 [range, 1-9]).

Conclusions: We showed that the heterogeneity in the genetic background of indeterminate thyroid nodules corresponds to their histopathologic diversity. The role of KDR as a possible malignancy marker needs to be confirmed. Glass slides with FNAB samples may constitute a reliable source of genetic material for NGS studies, providing a better insight into the molecular profile of thyroid nodules.