BRAF V600E assessment by pyrosequencing in fine needle aspirates of thyroid nodules with concurrent Hashimoto's thyroiditis is a reliable assay

Detection of BRAF mutation in cytology specimens has been proposed as a diagnostic adjunctive tool in evaluation of thyroid nodules with indeterminate cytology findings. Concurrent papillary thyroid carcinoma and Hashimoto's thyroiditis (HT), a disease characterized by thyroid lymphocytic infiltration, is a frequent occurrence. A large lymphocytic infiltrate might reduce the sensitivity of methods employed to detect BRAF mutation in thyroid cytology specimens. To determine whether testing for BRAF mutational status in fine needle aspirates (FNA) is reliable also in the presence of HT lymphocytic infiltration, we assessed the BRAF status by direct sequencing and pyrosequencing in a series of FNAs with and without concomitant HT lymphocytic infiltration. We also performed the same assessment by pyrosequencing in the corresponding tissue samples. Pyrosequencing demonstrated to be more sensitive than direct sequencing. The percentage of mutant BRAF ^V600E alleles was higher in FNAs than in the corresponding tissues, probably because of the lower stromal contamination in FNA than in the sections. In the presence of lymphocytic infiltration, the percentage of mutant BRAF ^V600E alleles determined by pyrosequencing was higher in FNAs than in the corresponding tissue samples (P <0.0001), indicating a minor lymphocytic contamination in FNA. The diagnostic value of BRAF ^V600E in inconclusive FNAs was not hampered by thyroid lymphocytic infiltration. These results indicate that BRAF ^V600E assessment by pyrosequencing is a reliable assay useful to refine inconclusive cytology of thyroid nodules also in the presence of concurrent HT.