DICER1 mutations in Bethesda category II, III, and IV thyroid nodules: A mutually exclusive relationship with BRAF V600E mutation

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Abstract Background This study aimed to investigate the prevalence and cytological features of Dicer 1 , Ribonuclease III ( DICER )‐mutant fine‐needle aspiration (FNA) specimens in thyroid nodules classified as Bethesda II, III, and IV categories. The authors also sought to explore the relationship between DICER1 and BRAF V600E mutations in Bethesda III thyroid nodules. Methods The authors collected a series of consecutive FNA cases diagnosed as Bethesda category II, III, and IV from a medical center over the course of 1 year. DICER1 exons 24 and 25 and TERT promoter mutations were detected by Sanger sequencing in all cases, and BRAF V600E mutations were detected by amplification refractory mutation system PCR in Bethesda III and IV cases. Results A total of 899 patients were included in the study. DICER1 mutations were identified in 52 patients: 20 in Bethesda category II (6.2%, 20 of 322), 25 in Bethesda category III (4.9%, 25 of 510), and seven in Bethesda category IV (10.4%, 7 of 67). Among the 510 Bethesda III FNA samples, 76 harbored the BRAF V600E mutation and 25 harbored DICER1 mutations. BRAF V600E and DICER1 mutations were mutually exclusive. In Bethesda category II and III cases, patients with DICER1 ‐mutant nodules were younger and had larger nodule volumes compared to those without DICER1 mutations. All DICER1 ‐mutant Bethesda III FNAs were classified as atypia of undetermined significance (AUS)‐other. TERT promoter mutations (c. ‐118G>T and c. ‐144 C>T) were identified in two FNA samples. Conclusion The findings of this study suggest that DICER1 ‐mutant nodules are unlikely to be BRAF ‐mutant carcinomas. Further study of the molecular characteristics of DICER1 ‐mutant FNAs will contribute to more accurate cytological diagnosis.

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