BRAF and RAS Mutations in Follicular Variants of Papillary Thyroid Carcinoma

Follicular variants of papillary thyroid carcinoma (FVPTC), particularly the encapsulated subtype, often cause a diagnostic dilemma. Therefore, many FVPTCs are interpreted as "indeterminate" in preoperative fine-needle aspiration (FNA). The aim of this study was to analyze the genotypic changes in BRAF codons 600 and 601, as well as the N, H, and KRAS codons 12, 13, and 61 in FVPTCs and investigate the usefulness of preoperative BRAF and RAS mutation analysis as an adjunct diagnostic tool along with routine FNA. Surgically resected thyroid nodules were reviewed to establish the histological diagnosis of FVPTC. All preoperative FNA diagnoses were categorized according to the Bethesda Reporting System. Mutations in BRAF codons 600 and 601, and N, H, KRAS codons 12, 13, and 61 were analyzed by pyrosequencing. Of 132 cases, 81 (61.4 %) had a point mutation in one of the BRAF V600E, BRAF K601E, or RAS oncogenes; BRAF V600E in 43(32.6 %), BRAF K601E in three (2.3 %), and RAS in 35 (26.5 %) cases. All mutations were mutually exclusive. Of 78 cases with an FNA indeterminate category diagnosis, 51 (65.4 %) were positive for mutations: 24 for BRAF V600E, 3 for BRAF K601E, and 24 for the RAS gene. The KRAS mutation was more frequently found than the HRAS mutation, comprising 22.9 % of the RAS mutations, and all KRAS mutations were located at codon 61. This study demonstrated that either BRAF or RAS mutations were present in two thirds of FVPTCs and these mutations were mutually exclusive.