Pyrosequencing analysis for detection of a BRAFV600E mutation in an FNAB specimen of thyroid nodules.

BACKGROUND

Fine-needle aspiration biopsy (FNAB) is the primary means of distinguishing benign from malignant and of guiding therapeutic intervention in thyroid nodules. However, 10% to 30% of cases with indeterminate cytology in FNAB need other diagnostic tools to refine diagnosis.

OBJECTIVE

We compared the pyrosequencing method with the conventional direct DNA sequencing analysis and investigated the usefulness of preoperative BRAF mutation analysis as an adjunct diagnostic tool with routine FNAB.

METHODS

A total of 103 surgically confirmed patients' FNA slides were recruited and DNA was extracted after atypical cells were scraped from the slides. BRAF mutation was analyzed by pyrosequencing and direct DNA sequencing.

RESULTS

Sixty-three (77.8%) of 81 histopathologically diagnosed malignant nodules revealed positive BRAF mutation on pyrosequencing analysis. In detail, 63 (84.0%) of 75 papillary thyroid carcinoma (PTC) samples showed positive BRAF mutation, whereas 3 follicular thyroid carcinomas, 1 anaplastic carcinoma, 1 medullary thyroid carcinoma, and 1 metastatic lung carcinoma did not show BRAF mutation. None of 22 benign nodules had BRAF mutation in both pyrosequencing and direct DNA sequencing. Out of 27 thyroid nodules classified as 'indeterminate' on cytologic examination preoperatively, 21 (77.8%) cases turned out to be malignant: 18 PTCs (including 2 follicular variant types) and 3 follicular thyroid carcinomas. Among these, 13 (61.9%) classic PTCs had BRAF mutation. None of 6 benign nodules, including 3 follicular adenomas and 3 nodular hyperplasias, had BRAF mutation. Among 63 PTCs with positive BRAF mutation detected by pyrosequencing analysis, 3 cases did not show BRAF mutation by direct DNA sequencing. Although it was not statistically significant, pyrosequencing was superior to direct DNA sequencing in detecting the BRAF mutation of thyroid nodules (P=0.25).

CONCLUSION

Detecting BRAF mutation by pyrosequencing is more sensitive, faster, and less expensive than direct DNA sequencing and is proposed as an adjunct diagnostic tool in evaluating thyroid nodules of indeterminate cytology.